Place it just before the door opens in your edit, then follow the reveal with Vine Boom for a comic entrance or Dramatic Dun Dun Dun for a horror reveal, keeping the knock as the cue that starts the scene.
About this sound
This clip is a run of firm, repeated knocks on a wooden door, lasting about nine seconds and sounding close and unmistakable. It creates a sudden sense of anticipation, as if someone is waiting just outside and expecting an answer. That waiting feeling can turn playful in a prank, awkward in a skit, or tense in a horror edit, depending on what follows the knock.