My rogue has Identify skill at 55, how do I use this? From general searching all I've found is people saying rogue's don't have identify til BT3, (I'm playing 1) but if that's the case, then why is the skill listed?

I believe the skill being listed is a bug.

(With that said, I don't think it would be unreasonable if the developers of the remaster gave Rogues this ability in the first two games; the class isn't that good, and this ability doesn't seem like it would be game breaking.)

The skill is used to identify the type of trap set on a treasure chest. That way you know which trap to disable.

Identifying an item by a rogue is not implemented.

Sometimes, early in the game, my rogue failed to ID a trap on the chest, but one of my other (non-rogue) characters was able to.

As far as I remember, if a rogue doesn't ID a trap, they never tell you the wrong trap type. They just say "I found nothing."