Hard to say. Sometimes stories like 'Knock Knock' blend elements of truth and imagination. Maybe it has some roots in reality, but could also be largely made up for entertainment.
A 'knock knock' full story can be a long sequence of 'knock knock' jokes strung together. Let's say we start with 'knock knock', 'who's there?', 'Lettuce', 'Lettuce who?', 'Lettuce in, it's cold out here!'. Then we can follow with another one like 'knock knock', 'who's there?', 'Canoe', 'Canoe who?', 'Canoe help me with my homework?'. These jokes are simple yet can bring a smile or a laugh, and when told in a row, they make for an entertaining 'full story' of sorts.
In fact, 'Knock Knock' is purely imaginative. It was written and developed from the creative minds of the writers and not inspired by any true incidents.
You can start by using 'knock knock' as a buildup to a surprise or a mystery. Maybe have a character hear the knocks and wonder who or what's behind the door.
The origin of 'knock on wood' is often associated with superstitious beliefs. One theory is that it has its roots in pagan religions where trees were seen as having spiritual significance. People would touch or knock on wood to invoke the protection or good will of the spirits associated with the trees.
I'm not sure specifically as there could be many stories named 'the knock'. It might be about a mysterious knock on the door which could lead to a series of strange events, like a character's encounter with an unexpected visitor or the start of a spooky adventure.