There are a few Traits that add precision damage. I know of one from Humans from Golarion but can't seem to find its name at the moment.
Some class features call out their additional damage as precision damage (read: Pistolero), but there are not that many.
Why do you ask?
I am currently playing a Stonelord and they get an ability called Stoneblood. This is what is does:
At 3rd level, a stonelord's vitals begin to calcify and her blood transforms into liquid stone. She adds her paladin level on checks to stabilize at negative hit points and gains a 25% chance to ignore a critical hit or precision damage. This does not stack with fortification armor or similar effects.
Just not entirely sure when the precision damage would come into play, so I am trying to understand more.