It depends on a lot of things. Typically you don't want to use "outside" knowledge. So if you and the group are bullshitting before the session and you learn your paladin has high af perception you'd try not to let that knowledge bleed over into your character. But if it naturally comes up in the game "my paladin keeps passing perception checks that I keep failing" it'd be similar to noticing you have a really perceptive friend and you begin to trust their instincts a bit more and more.

The characters probably shouldn't know the exact stats, but I mean, some things are reasonably obvious. For example if the barbarian pc turned an enemy into mush with a single hit in the last battle, the character can assume that they're very strong. And so on.