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Thanks, Finoan! It's good that I get at least something out of what seems to be the weakest Investigator subclass or methodology :)

It becomes Offguard on both Critical-Success and Success, Whenever an outcome says that it has the same effects as another outcome that means in full with any modifications mentioned within. As the circumstance bonus being +2 instead.

The bonus is also to Perception DC as you are not the one rolling the secondary check in this scenario you gain offguard regardless of any Lie to you.

Summary,
Offguard on both Success and Critical Success.
Offguard regardless if the creature truthfully answers, successfully lies, or fails to lie to you when answering your question.
(Otherwise you would've known the creature was lying if you failed to detect the lie)

Thanks, NorrKnekten, that clears everything up!

Pointed Question:
"You ask a question that charms or needles someone in just the right way. Ask a question of a non-allied creature that you can see. Attempt a Diplomacy check against the creature’s Will DC. The creature is then temporarily immune for 1 hour.

Critical Success The target must directly answer your question. It doesn't have to answer truthfully, but you gain a +4 circumstance bonus to your Perception DC if the creature attempts to Lie to you. Whether it answers truthfully or not, you glean something from its body language, and it is off-guard to the Strike you make using Devise a Stratagem against it before the end of your turn.

Success As critical success, but the circumstance bonus to your Perception DC is +2.

Failure The target can refuse to answer you as normal.

Critical Failure The target can refuse to answer you as normal, and its attitude toward you decreases by one step due to your aggravating attention."

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I am not entirely clear whether the creature becomes off-guard both on Critical Success and Success, or only on Critical Success.

I am also not clear whether the creature becomes off-guard only if you besides succeeding on the Diplomacy check also succeed on the Perception check to determine whether it is lying or not.
The rule says, "Whether it answers truthfully or not, you glean something from its body language...", but I am not sure whether that means that you get that bonus even if you fail in determining whether it is lying or not.