You can use your knowledge to exploit your foes' weaknesses and overcome their strengths.

Knowledge (any) 5 ranks

Upon selecting this feat, you immediately add one Knowledge skill of your choice to your list of class skills. Thereafter, you treat that skill as a class skill, regardless of which class you are advancing in. Whenever you fight a creature, you can make a Knowledge check based on its type, as described on page 78 of the Player's Handbook, provided that you have at least one rank in the appropriate Knowledge skill.

You then receive an insight bonus on attack rolls and damage rolls against that creature type for the remainder of the combat. The amount of the bonus depends on your Knowledge check result, as given on the following table.
Check Result Bonus Granted
15 or below +1
16-25 +2
26-30 +3
31-35 +4
36 or higher +5

You can make only one Knowledge check per creature type per combat. If you fight creatures of multiple types during the same combat, you can make one Knowledge check per type, thereby possibly gaining different bonuses against different opponents.

Example: Alhandra faces a black dragon, a vampire, and a beholder. She has the Knowledge Devotion feat and ranks in both Knowledge (arcana) and Knowledge (religion). At the beginning of the battle, she makes checks to gain bonuses against the dragon and the vampire, but since she possess no ranks in Knowledge (dungeoneering), she has no chance to gain a bonus against the beholder (an aberration). Alhandra's Knowledge (arcana) check grants her a +3 insight bonus on attack rolls and damage rolls against the black dragon. Later, a half-dragon enters the fray. Alhandra cannot make another check since she has already checked for the dragon type this combat, but she can apply the +3 insight bonus to her attack rolls and damage rolls against the half-dragon as well.

This benefit is an extraordinary ability.