This skill feat states:
Prerequisites: expert in Arcana, Nature, Occultism, or expert in Religion.
You rarely misidentify an item. When using Arcana, Nature, Occultism, or Religion checks to Identify Magic, if you roll a critical failure, you get a failure instead.
It seems like RAI you would need to be expert in the applicable knowledge skill in order to able to benefit from Assured Identification, but looking at the language of some of the other skill feats, it is not so clear to me.
For example, the Quick Recognition skill feat states:
Prerequisites: Recognize Spell; master in Arcana, Nature, Occultism, or Religion.
You Recognize Spells swiftly. Once per round, you can Recognize a Spell using a skill in which you’re a master as a free action.
That feat specifies you need to be master in any skill you intend to use for this feat. Assured identify has no such language of "in which you are expert." So does this mean you can use it for trained-only skills?
As an example, a character is expert in Arcana, meeting the feat's prerequisite, so he takes that skill feat. He is also trained in Nature and wants to benefit from Assured Identification when making a Nature check to identify a magic item with the primal trait. Does this work? How would you rule it?
Best Answer
You can use any of the skills.
The feats text itself answers your question:
(emphasis mine) The skill feat explicitly says that you do this when using any of the 4 skills (if you are at least Trained, because the Identify Magic action requires you to be Trained). If it were limited to a single skill or to skills where you are expert or better, it would say so (and would probably also allow you to pick it multiple times for different skills). One example of this is the one you cited, but there are others out there, e.g. Assurance, which specifically includes the line "Choose a skill you’re trained in." and limits its usage to that skill.