Knowledge checks are a bad example. A knowledge check in D&D will take IC information and hand it to the player, who can then OOC make a decision based on it.
There is nothing that requires you to have Knowledge in order to know something. Knowledge checks are completely metagame. For instance, if I fail my "know what hurts trolls" roll, I can still learn through play that fire hurts them, and in the future, I will not roll to know it again, nor has my Knowledge (nature) increased. Further, upon meeting a drow for the first time, my elf ranger can blurt out, "My father died in battle against these evil elves! They live beneath the ground and have strange powers. Their queen is a demon goddess named Lolth," and there is nothing in the rules to prevent it.
In fact, it may be necessary. Suppose your campaign starts at level 11, and your character has been allowed to take a PrC with a requirement that you have helped slay an adult dragon. In this case, it has been agreed that it was a red dragon. Now, if you encounter red dragons later, is the GM going to make you roll to know that red dragons breathe fire and can cast spells?
What if I have a ranger with favored enemy (lizardmen)? Do I need to roll in order to know that lizardmen often have druids as leaders? If my favored enemy is dragons, do I have to roll to know that some dragons change shape?
If metagaming is to disallowed, the FIRST thing to do should be Knowledge checks. They are a metagame tool. Simply knowledge, distinct from the ability to do something, is completely an IC decision.