The Knowledge skill represents deeper specialization in a chosen subject. A dwarf with Knowledge (Stonework), for example, not only knows the dungeon was carved, but might just know what race did it and the era in which it was first excavated. He might also be able to locate stress points that can cause a cave-in! Knowledge of a particular region is also handy. In a fantasy campaign, for example, locals might know the Dread Mountains are home to vicious harpies. A hero with Knowledge (Dread Mountains) might know a safe route or the specific peak the creatures' aerie is in.

Knowledge skills should be used for subjects that have a significant impact during the game. If the subject comes up very rarely, use Common Knowledge instead.

Savage Worlds Deluxe Edition p. 23