The dragonstone does seem to be a map of Skyrim with various locations singled out. The back of it has some dragon tongue script which he cannot decipher—except for one word, which he mysteriously can: Alduin. But he doesn't seem to instinctively recognise the symbols themselves, only the whole word. It does seem like the word has exactly six runes, though, so if he assumes they in fact match the letters in Cyrodilic he can find some correspondences on the rest of the text. Not enough to be able to sound it out, and most certainly not enough to be able to understand it, but it occupies him for a little bit while he tries to suppress a minor freakout.

He's not sure why the freakout. He already knew he was Dragonborn, two separate people had told him and he instinctively learned a magic word in the dragon tongue and had a vision of a dragon. But something about the dragonstone and the word he learned there makes it all feel much more... real, somehow? He recognised the word he'd just learned in the Shout that draugr was using—fus ro dah—and it kind of hit him that that's a thing he'll be able to do. And it's not the same as magic, the Thu'um are a different thing, a lot more fundamental to the universe than magic. It really is happening, he really is Dragonborn and he has to stop the dragons. He's returning to Whiterun to give the court wizard a map to where dragons have been buried and then he's gonna have to... fight them, or something. Do something about it.

Aah.

He maybe kind of understands Onmund a little bit better, if Onmund managed to fully internalise the whole "Dragonborn" thing immediately like that.

Nothing to it, he supposes. To Whiterun.