Put it just before the reveal in your edit, then follow the payoff with a game show buzzer for a wrong answer or a scream meme when the reaction is pure panic. Use it once per scene, and save it for the biggest twist rather than every small surprise.
About this sound
This clip plays three slow, low 'dun' notes in a row, stretched out for about five seconds with each hit landing heavier than the last. It feels tense and ominous at first, then funny once the pause lets everyone realise something big is about to happen. It is the go-to sting for a reveal, a twist or a very bad decision.