wikipedia is probably more reliable than most offline encyclopaedias (which would still list Pluto as a planet, for example…or Michael Jackson as a black “boy wonder”). It has up-to-date information about everything, and, even though some of the newer articles might contain inaccuracies, so do the same articles in any other source of information.
If you care enough about something, you can keep reading until you discover all possible discussions and views about the subject (like the question of the “four Johns” above, which, after some more research, I found a lot about on wikipedia itself).
But the best thing about it is that, like any encyclopaedia, you can get a general idea of what it’s all about (eg if you’ve never heard of Nubia, just type it and read several pages about it. Now if you’re interested enough you might want to take a course at university and write a PhD on it, but until then, wikipedia will have at least helped you figure out it’s a country and not a mineral).