Ok, I am late and I am cheating. I am literally copying and pasting from a similar question. Hate my laziness if you wish.
It's another wiki answer, but it includes the importance of not just linking (as any wiki does), but making it searchable, because after a while, this gets big enough to make it harder to find stuff. Like, over a thousand pages, and you don't remember where things were written when...
OK, pasting away...
I'm playing the "Very Late Answer" game again. But I run a very, very detailed old game. So this issue is one I am familiar with. And I am a believer in trying to create as immersed a game as possible, and this means having players be able to think 'in-character'...which they CANNOT do without having some level of in-game knowledge.
A lot of these are good answers. I also give out of roleplay experience, and tailor it around using 'in-game, immersed' knowledge. It is a good reinforcer.
But one of the most useful things I did is create a searchable wiki for the game and for pertinent data. It also includes the rules and such we use. And this is pretty easy these days. All my players have tablets or laptops, and this way, when a player or the Gm mentions the Dockside Area of Igbar or Chorm, the other players can look it up online quickly.
Wiki's also accumulate nicely over time, so if a GM puts in a little bit at a time, before you know it, you start to get a nice database for the players to use.
Wiki's can also be set up so that players can elaborate or make their own pages, which means they spend even more time on the game wiki. Here is one from an online group I run.
Finally, Wikis are not just searchable, but linkable. So players can keep handy links of their spells or skills or important maps, etc. I often set up player-specific links based on skills or requests of better players so that the more inqisitive players actually have more knowledge.