Necromancy

consider <monster>

Necromancy is knowing the undead: zombies, skeletons, ghouls, ghasts, wights, spectres, vampires, liches and ghosts. It works by itself when you consider one of them: you are told what it seems to be, and get an estimate of how it compares to you (its hit points and armor class, and the better you know the lore, its attacks, its damage and its to-hit and damage bonuses).

No class learns it with its levels: a teacher out in the world teaches it, for gold, and considering the creatures it knows teaches you a little more now and then. The Character pane's Skills tab lists it under Other, with who teaches it and where.