Trick Magic Item shows up in the feats lists for each of the skills associate with a magic tradition - Arcana, Nature, Occultism, and Religion. Most other skills, such as Assurance, only apply to one skill even if they could be selected for multiple.
Trick Magic Item in 1 Feat
Trick Magic Item is a single skill feat. You can read it on page 268 of the Core Rulebook where it appears printed only once.
The text of the feat makes it clear that this feat applies to all 4 magical tradition skills (Arcana, Occultism, Nature, and Religion). There is plenty of precedent for this, such as the Quick Recognition skill feat1.
It sounds like part of your confusion stems from how you located the feat on the Archives of Nethys. Odds are the site's developers added Trick Magic Item to lists for each of those four skills, so that users could find it where they intuitively expect it to be. It's an artifact of representing a book within a database table.
1 For an list with more examples, see Ifusas's answer.
Trick Magic Item is one feat
Trick Magic Item lacks the crucial line in other "multi-skill" feats,
Choose a skill you’re trained in.
Trick Magic Item applies to all four of the skills, but is only one feat to take. This holds true for the other magic-tradition feats
*This one is less likely to apply to more than one