Knowledge skills are used to gain insight on subjects, depending on the knowledge chosen. While there is a concrete list of a few knowledge types here, characters can come up with their own Knowledges at the GM's discretion so long as they are just general enough to have a proper application. Example, Knowledge (Humanoids) would work for identifying humanoids and their types, yet Knowledge (Life Forms) wouldn't tell you about humans but rather tell you general facts about how various humanoids live and exist. They may overlap in some uses, but try not to make them overlap too much.
Identifying a creature with a Knowledge requires you to make a check equal to DC 15 + Creature's Effective Level.
Especially common creatures reduce this DC by 10 (such as animals, vampires, most humanoids, and so on). Rare creatures increase this by 10 (such as Satori, most creatures above EL 20, and creatures not widely known in the land).
Success gives information about the creature and its lifestyle. Failure may yield false information, or generally unhelpful information. Alternatively, the character could learn something about the creature but some of the information is misleading. Example, figuring out a creature is weak to a certain type of metal but thinking the metal is Steel instead of Cold Iron.
This uses Smarts as an ability.