Local Wei Wuxian did not intend for his notes to be used as a basic guide on cultivation so nothing is laid out in neat reasonable ways.  Some of them are notes on ideas in progress and contain theories that are later confirmed or dropped; Wei Wuxian did not timestamp his notes or put them in chronological order at any point, and also didn't often go back and add notes to his personal notes if a theory was later invalidated. 

There's a page mentioning that Jiang Cheng is getting frustrated with how few of his cultivators have formed their golden cores, even though they both know it takes four years on average - not everyone is as fast as them!  They are formed in the lower dantian.  It definitely involves meditation, and needs instructors to watch over them as they do it "so the kids don't make their cores upside down just because they can't see what they're doing yet."

Wei Wuxian makes occasional references to learning techniques but he doesn't go into detail on something so obvious to him.  There are no references to learning a technique then not being able to use it.

"For concerns: Demonic cultivation is similar to using talismans in being too difficult for the mundane to learn, due to senses needed to see energy only granted by a golden core even if one isn't needed for its use," is written on one page otherwise dominated with sketches of decorative tassels.

Possible theories for rebuilding golden cores in people who had theirs destroyed are circled around to multiple times but don't seem to have gotten anywhere.  "sending Jiang Cheng off to see Baoshan Sanren is a trick that would only work once, and there might be others around somewhere who can be brought in."  (Because Local Wei Wuxian does in fact know that Jiang Cheng can read his note-taking handwriting and might one day do so.  You just don't leave incriminating notes around!  And local Wei Wuxian knows what he means.)

Memorizing lots of techniques makes someone more versatile!  But apparently most cultivators find this hard.  There's a reference to "the usual set everyone in Yunmeng Jiang learns," but not a list of what that is.  Methods for communicating with ghosts, exorcising harmful spirits, and purifying areas are mentioned at various points and can be assumed to be included.  Also lots of sword fighting techniques, some of which sound like magic. 

He is not expecting a basic guide on cultivation (maybe he should have asked other Jiang Cheng for an actual basic guide - though maybe other Jiang Cheng would have told him to focus on his report or told him off for trying to pry into secrets - but he didn’t). And he knows what his notes are like. This is what he’s got! (On the bright side the notes are not likely to contain really stupid theories by overly important doms!)

The notes on golden core formation sound very ‘yep, learning power stuff’ to him. Ha, he was faster at local power use too. And so was other Jiang Cheng - what with local power use being what other House (sect) Jiang does, naturally he was. Was he faster though?

...apparently Baoshan Sanren is in some way an entity you can currently go see here? ...Ok he has no idea what that entire note means. 
Also apparently golden cores can be destroyed, which feels very weird! Other Jiang Cheng did say they were an organ or something like that right? And they’re in a place. Which is also really weird!

This is not going to be enough to let him definitely distinguish between his theories, though he does come up with some more theories and updates in various directions to the previous ones and acquire a bunch more material for his own not especially neat notes.

(He is guessing that, given other Jiang Cheng accusing his flute of evilness, the flute-playing-for-controlling-‘resentful energy’, and that name, that demonic cultivation might be the flute one.)

Wandering around the room with a sheaf of notes (he’s limping less now, though still some - Lan Zhan might have scolded him a bit, but he has been being (mostly) still for a while today, ok) his eyes happen to fall on the fruits other Jiang Cheng had left. Oh, yeah, fruit breakfast, he should eat those.

Somewhat later, finished with a set of notes, he sees and remembers about the fruit again. Right, food! This time he gets all the way over to the fruit. Are they at all interestingly alien fruit? Historical fruit? Somehow-affected-by-different-power-use fruit?

Historical fruit!  If his world has the same flora as Earth he will be able to recognize the approximate genus of the plants if not the specific cultivars - persimmon and pear and so on.  They're far from wild but have had fewer iterations of selective breeding than he might be used to, their seeds a bit larger and more numerous.  There's nothing magical about them.  Lotus Pier harvests its eponymous lotus but other than that cultivators don't do much in the way of farming food and farmers don't have magic. 

At some point in the morning a servant crosses through the courtyard to deliver supplies to Jiang Cheng's room, but they have no reason to pass particularly close to Wei Wuxian's door. 

(Unless it happens sufficiently loudly or sufficiently magically-with-a-range, Wei Wuxian is going to have no idea of what is or might be happening beyond his door.)

'Fruits and their cultivars and history' happens, in fact, to not be one of the random areas he knows much random amounts of information about. It's not obviously alien fruit, like sparkly crystal fruit or coiled-spiral fruit - probably predictably, given everything else, and also he would have noticed that earlier. Coming all the way up close and picking up some fruit fails to reveal any more subtle obviously alien fruitless, and it turns out it's kind of hard to tell the difference between 'same basic fruit but different because historical' and 'different fruit but similar because fruit evolution'. But it is different from the fruit he usually has, which is neat. (He does check it all for magic - he's not expecting magic fruit that much, but if it is magic fruit he's definitely not going to miss it!)

He munches on some fruit wandering around the room some more, then comes back to sit on the floor against the bed, tosses his next fruit up and catches it before taking a bite. The picture of Lan Zhan from other him's notes has ended up face up partially on the pillow at some point; he smiles at it with his next bite of fruit-breakfast.

...and then it hits him, really hits him, that from the point of view of everyone back in his own world he vanished into thin air or bizarre magic out of his room at music camp, and no one is going to know where he is or what happened to him or be able to find him if they look for him.

He swallows. (He isn't actually sure if there's fruit in his mouth or not). Fuck. 

He - has no idea one way or the other if the nonvolitional-and-it-turns-out-interworld teleportation left any trace from the other end, or even if it did how long a trace would last. If there's no trace - the music camp is going to think he's snuck out, again, and look for him or wait for him to show back up. He can't remember at which point in him not showing back up they have to tell Jiang Cheng, but at some point they're going to have to tell Jiang Cheng.

Who will probably think he snuck out and then got into something stupid. Or else is going to think he's actually run off. - That's fine, really, it's not like a bulletin about him being a runaway is going to do anything to him while he's here and he didn't run off and he can prove it. 

He closes his eyes and feels like he can still see that picture, see his own Lan Zhan's face. Lan Zhan. Someone is going to tell Lan Zhan, and Lan Zhan will think he - just decided to do it, and didn't even talk to him first, didn't even tell him first. And - his Lan Zhan is too good to him, always thinks better of him than he deserves, his Lan Zhan is going to think he must have had a reason, must have had a good reason to suddenly change his mind so much and then just go ahead and do it right then. (Lan Zhan - Lan Zhan has to know, right, he wouldn't just disappear, he wouldn't just leave him, that if he did suddenly decide he had to get out that he'd find some way to contact him, somehow, just as soon as he could...) 

If there is a trace, if it's as what-is-this as what he got from his end - or even if it somehow isn't - no one's going to think he did that. (OK some people might think it a little. But not really, not for real). So everyone's going to think he was kidnapped, by someone with fucking teleportation. 

- Lan Zhan will worry so much. He wants to hope it's the other one, just for that. Except Lan Zhan will worry about him anyway, even if everyone says he ran off will worry he actually snuck out and ran into something, will worry about him off being a runaway submissive, will think he had a reason and will worry about what happened.

Shijie will worry.

(His Jiang Cheng will worry. If he got to see that he'd expect to find it somewhere behind 'wanting to fucking kill him' (not literally) in the first case and 'wanting to fucking kill whoever took him' (absolutely literally) in the second case, but - he does in fact know that.)

(Uncle Jiang will - think he's failed in his duty to his parents. And worry.)

- He tries to remember what the betrothal rules are. How long are the terms if something happens - does it matter if he's a suspected runaway, if it's different does there need to be proof, does it matter if it looks like something happened but no one can find him -.

It has to be a while, that's how contracts like this work. It has to be a while, so no one's going to be trying to get Lan Zhan to marry someone else, because he can't just be gone for that long anyway, that's too long, Lan Zhan will, Shijie will -

He draws his knees up to his chest, puts his arms around them. Maybe everything's fine, really, and this is one of those interworld travel setups where time doesn't pass in his world while he's here and when he comes back no one will even know he was gone anywhere. Or time passes really slowly and it'll have been an hour and one of the doms will be yelling 'Wei Wuxian, if you're up there again -' into the attic with all the abandoned instruments.

What if it's the other way around and even if he and other him figure out the way back really soon it'll have been a hundred years -

He sits up, sets his jaw. No, absolutely not. He does not care what interworld travel rules turn out to say, that is not going to happen. He's in another world, so he got here, so that happened somehow and it's possible, and he's got two worlds' power use systems, and other him is holding borders and invented a whole new form of cultivation, (and he knows he understands computational power analysis better than at least half the doms who get themselves published about it, and that's not counting what he hasn't even seen published anywhere). They're going to figure out this interworld transportation, and if time thinks it should have been a hundred years he's going to invent a version with time travel, and if that's not how interworld travel is supposed to work then it can go and drown itself in a lake and he's going to get back to his Lan Zhan. 

He stands up. (The fruit, partially eaten, ends up somewhere by the bed, and he has basically forgotten about it.) Stacking up a pile of other him’s notes, he heads for the desk, where he applies himself to the pile with a new line of fervor.

For the next while, the room will have no activity other than Wei Wuxian absorbed in the notes with Wei Wuxian intensity, mostly at the desk, occasionally pacing again or in some stranger position.

He first notices that he has a problem when on his latest turn of pacing he - must have gone higher intensity pacing without noticing it - and sets his foot down hard enough to jar his ankle. That gets him a jolt of pain strong enough to get through his (currently extra heightened!) threshold of ‘ignore all that’ and stumbling enough he almost trips onto the floor. Ow. He lifts his foot and bends down to rub at his ankle. (Yep, Lan Zhan would definitely scold him. And help him kiss it better.) (- Nope, no sadness, he’s going to get back to his Lan Zhan and tell him all about his other world adventures.)

Alright, he maybe needs to take a break with the pacing. He goes back to the desk, sits down to refocus on the notes.

Refocusing on the notes turns out not to work very well.

Sitting back at the desk also turns out not to work very well. He wants to get up again immediately. He wants - 

He moves two notes, picks up another page. His brain does not cooperate with the next step of the process. He feels like there’s a wire running through him, through his body and his head. He wants to get more up then getting up.

- in retrospect now he can notice this is one of those been-building. Yep, here are his more recent notes gaining more doodles escaping the margins as they go on, drawings getting more aggressive. If he’d been using ink he knows his brushstrokes would have been going everywhere. As it is he may have almost dragged a hole through his paper. His pacing didn’t leave that kind of physical evidence, but while his ‘noticing stuff while absorbed’ is, exhibit one, possibly not so great, his ‘what he did ten minutes ago’ memory isn’t that bad.

Kind of unfortunately, he is now not too absorbed to notice stuff. 

He wants to get up, he wants to get more up than getting up, he wants to walk - he wants to walk and keep walking.

He does stand, paces a round across the room, favoring his other leg. He turns at the wall, he turns at the other wall, at the bed, at the door. He wants to walk and keep walking, he wants to walk through the wall, he wants to shove himself through the door if he has to. 

The walls feel like they’re kind of closing in on him again. He wants to jump out of his skin. 

He throws himself down on the bed (gets up again a few seconds later). Ah, fuck. - It isn’t fair, he’s not even standing at a wall or anything, it’s not like he’s having to copy horribly boring etiquette lectures, this is other him’s magic notes that’s as much directly opposite from boring as you can get!

(He tries to pick up some notes again and do something beyond the step of looking at the piece of paper and wanting to jump out of his skin some more. This continues not to really work at all.)

- And it would be fine if he could walk and the door wasn’t in the way. If the air was moving, if there was something to see and listen to, if he could do something, if he could talk to someone - he doesn’t even need to actually do it. He is 100% confident that if he were looking at these same notes sitting on the roof everything would be working just fine. Unfortunately -

He knocks his head back against the wall. It’s not like he doesn’t get confined to his rooms all the time at home! But - first of all his rooms are bigger, which he doesn’t usually think about in this context but apparently turns out to matter. And have his belongings in them, some of which he has on some level selected to be good for this kind of situation. And he’s usually allowed out in the courtyard. And sometimes even allowed very specific phone privileges, or to talk a bit to the servants. And usually he does not have to be quiet on pain of execution-worthy political problems for people around him, so if he decides to turn cartwheels while singing themed credits music the most that’s going to happen is someone shows up with a ruler.

- And generally when he’s confined to his rooms he’s had his hide tanned first, which he also doesn’t usually think about as an important factor but also clearly turns out to matter.

(And if he really does need to (also if he doesn’t) he can in fact go ahead and just leave, and if he doesn’t get caught that’ll solve his problem, and if he does get caught that’ll solve his problem a different way.)