Need some help picking a skill

[LoneStranger]

I've tried to look up the answer on my own and I can't find anything that's really giving me the answer I need so I'm hoping I can get some help here.

I created a Ninja character that was smuggled out of Chu Ye at a very young age and after hearing the stories has grown up to hate Oni and wants to take them down a peg or two, but I don't know what skill to give the character to know how to ID them. I was thinking Knowledge: Planes but since they're considered Native Outsiders would Knowledge: Dungeoneering help instead?

[Jayson Klein]

Either Knowledge Planes, Knowledge Religion (they are "demons" in ancient lore), or Knowledge Nature (since they are.... found.... walking around and stuff, lol)

[Pendagast]

dungeoneering is more about the dungeon itself. Just let the DM tell you what skill he would use to determine that.

[LoneStranger]

Yeah I'm thinking Knowledge: Planes might be the best one. I was thinking of using a skill that would be good for that one reason but would generally be totally useless everywhere else.