Put it at the start of a scene, just before the door opens, then follow it with the Vine Boom for a reveal or the Dun Dun Dun for an entrance, and save the SpongeBob Fail for when nobody answers.
About this sound
This is a short knock on a door, lasting about a second and a half, made for a quick, attention-grabbing moment. It feels sudden and expectant, like someone waiting outside who wants an answer now, and it works because the sound is instantly familiar. The clear, close knock cuts through a quiet moment and makes people turn toward the door.