I make no attempt to separate the two. It's artificial and doesn't really contribute to the fun. Might as well say, "This character isn't going to use any words with the letter 'q'..."
It's no more artificial than your character may be trained in Arcana and you are not. Your character has abilities and skills. They don't overlap with your knowledge. I can tell you how to make gunpowder but that doesn't mean my character can.
Let me give a couple of examples. When I was in college, I had a DM who ran multiple different groups in the same world at the same time. Things happening in one group could affect others. Plus time would not be perfectly sync - group A could spent 3 weeks traveling in half an hour while group B was in a dungeon crawl for four sessions before taking some downtime and resyncing. Several people were in multiple of groups depending on availability.
If one of us would suddenly start looking for anti-undead items and stocking up on holy water because we knew that a wraith scare in another group blew up and was spreading towards our location that would be really cheesy.
Another example - we had one DM who read and ran modules for his group and was a player in a group I played in. If he suddenly knew the traps, and that under the fountain was a secret treasure cache, and the BBEG had weakness if we smash these statues in another room, that would have sucked the life out for the rest of us.
This doesn't mean you can't use anything. Skeletons being undead should be obvious. As a DM if you have an appropriate trained skill or background you can justify a lot. "Hey, I'm a bard, any heroic stories about using fire to defeat trolls floating around?"
But there are times you really need to keep what you know as a player off of the game for the enjoyment of everyone in the group.