An interrogation scene is a role-playing scenario where one person knows some information that the other person is trying to find out. The trick to an interrogation scene is to have some specific piece of information, which the submissive partner knows but the dominant partner doesn't. A good way to do this is to shuffle a deck of cards and have the submissive secretly look at the top card in the deck; the dominant's job then becomes to get the submissive to say what card it is.
A basic interrogation scene might start out with the dominant "capturing" and forcibly restraining the submissive, perhaps by stripping the submissive and tying the submissive to a chair or to the bed. The dominant then begins "torturing" the submissive to get the information. This "torture" can combine many of the ideas described here--clothespins, spanking, paddling, mock-"rape," and so on. If the submissive doesn't turn over the information, the dominant can keep escalating the interrogation, gradually moving to more and more intense activity, until the submissive cracks and tells the dominant the information.