| CMantle |
It can only be used against opponents. However, opponents does not mean "currently in combat with." There actually is not any official definition of "opponent" as far as I am aware. The place that I would reference to limit how you are allowed to use this ability is the Intimidate skill, which allows you to both 'Coerce Opponent' and 'Demoralize Opponent'.
Demoralize Opponent is primarily used in combat, to grant the shaken condition. However, Coerce Opponent is almost only possible to use *outside* of combat, since it takes minutes to perform and can be continued over a period of weeks.
That being said we have to consider what an opponent is. To use a general definition, an opponent is anyone with a goal contrary or different to your own. Is the shopkeeper trying to buy your item for as little as possible while you sell it for as much as possible your opponent? Yes. It would make sense that "studying" him would aid in your ability to bluff him into paying more for an item.
From this example you can draw 100 others. That being said, similar to casting "detect evil" on everyone you meet, studying an opponent is a *noticeable* activity. You are actively scrutinizing and watching them intently. If your GM knows how to GM he is going to punish you for constantly studying every NPC, most probably by attitude shifts or penalties to diplomacy checks and so on. Don't be that guy who spams his ability. Use your ability to study opponents against NPCs and creatures who you believe are *actual* opponents.