From Pathfinder Book of the Dead, which isn't enabled.

Slayer's Identification

FREE ACTION

Activity free action

Trigger You roll initiative and can observe a creature you know is undead

You attempt to Recall Knowledge to identify the undead creature with a +1 circumstance bonus. If you're a master in the skill you're using to Recall Knowledge, you gain a +2 circumstance bonus instead.

Pathfinder Book of the DeadOGL