I can't agree more with Dinesh. You cannot surely ask the candidates whether they liked the questions that were asked in the interview. Probably you want to know whether the candidates felt at home at the venue, liked the ambiance, or were well looked after by the support staff. As Dinesh said, this has more to do with the organizational culture.
If you still want to elicit feedback from the candidates to improve, you can give them a simple format with questionnaires on seating arrangements at the venue, the manners and etiquette of the support staff, and what they would like to be served, i.e., water, tea, and biscuits, etc. Additionally, you can ask about any other amenities they feel are missing at the venue, like a fan in the proper place (sometimes the chair will be in one place and the fan in another).
Regards, B. Saikumar