See, thats why I always try to have at least 1 point into most knowledges, so you can make that check. Sometimes you luck out with a good roll, but at the very least you can try. Look at the entries in the PHB, for the knowledges skills, on what creature types each identifies. Religion for undead, Planes for outsiders, Arcana for Constructs and Dragons, Nature for a bunch of shit, Dungeoneering for freaky monsters. Local, I think, for humanoids.
Damn, its been like 3 years since I've actively played, I'm suprised I remember some of this lol.
Good luck in your game, man. I've been following your threads, and I'd be hard pressed to not murder that DM.