Gnomes have this "Bewildering Koan" feat available to them:
As a swift action, spend 1 point from your ki pool and make a Bluff check by asking a creature one of the impossible questions you ponder when meditating. If the creature fails its check, you choose whether it loses its next action or you gain a +2 bonus on all damage rolls you make against that creature for 1 round.
The feat description says the target loses "its next action". SKR has clarified they lose "their turn".
So what can and can't a bewildered mark do? Do they still get Attacks of Opportunity? Can they Speak? Are they blocked from speaking, but having just failed their "next action" can now do anything again?
"Losing a turn" is not the same as being stunned or it would just say stunned. This means that we should not add anything more to the feat than is set out by it. Speaking is a free action that can be done off turn, so that seems to be allowed. An Attack of Opportunity can be done off turn as well, so that is still available. Anything that can be done off-turn would be available to them. This would be the RAW reading to me.
Now, as a GM, I would rule that they couldn't speak about anything other than the koan you just proposed as it is clearly their mental focus. They will defend themselves and take AoO's, but that would probably be it. I could see how a GM may rule that they cannot take AoO's either, but this is already a highly useful feat. For the sake of balance, I could not add anything further.