This is something I try to be very careful with. It's easy when one of my PCs literally fell from the sky at the end of spring: he knows nothing, Jon Snow.
Seven on the other hand is generally educated, literate, and came from a city where trade from the outside world is becoming more and more common. What does this mean? Well, he can read, he knows how Lhavit functions and he took an early interest in stars and cartography so he knows how to organize the sky on a grid and a few astral coordinates from summoners that he badgered at the Plaza. But, by no means is he worldly. There was no reason to learn who the Syliran Knights or the Icewatch were. There's no way he'd know of Wind Reach, or Blackrock, or say, Denval, because he has no way of really knowing those places exist. Being a foreigner for the complete period of his active roleplaying career, he can pride himself on knowing information about Lhavit that, say, a Syliran just wouldn't know, and that gives him a sense of being smarter than the average bear.
I'm sure I've assumed too much along the way. His best friend is from Ravok and despite there being implication that he's probably asked about the city (being curious as he is) I'm hesitant to actually let him use that information, because it never happened in thread.
Magic is something that escapes him entirely. It happens, but he's seen very little of it. Just recently he learned how to shield, but despite having a book on the subject he needed help to make such an intangible concept work.
I don't enjoy playing with people that assume their character is well-educated on a world that's generally quite isolated city-to-city. Half the fun of writing for me is the exchange of information, the pursuit of new knowledge.
This was longer than I expected it to be.