When speaking to an NCO, what position should you stand at?

The correct choice is to stand at "parade rest" when speaking to an NCO. This position demonstrates respect while also maintaining a level of comfort. In military customs and courtesies, "parade rest" allows for a more relaxed posture than "attention," which is a more formal stance used when addressing a superior officer.

Standing at "parade rest" involves having your feet shoulder-width apart, hands clasped behind your back, and your gaze forward. This position reflects a balance between alertness and ease, acknowledging the authority of the NCO while not being overly stiff.

The other options, like "attention," are more formal and may not be appropriate in all conversational contexts, as this position implies that you are being inspected rather than engaged in conversation. "At ease" is typically used when you're allowed to relax but can still be considered overly informal for speaking to a non-commissioned officer. "Sitting down" is also inappropriate, as it does not convey the proper respect due to an NCO during a discussion.