Well, family could be a theme. Maybe the story explores Harry's family or the idea of starting a family. Also, magic could be a prevalent theme if it's set in a magical world. It could play a big role in the events that unfold in the fanfic. Additionally, self - discovery might be a theme, with Harry learning more about himself as the story progresses.
I haven't really delved into 'Harry Knock Up' fanfic specifically. However, when searching for fanfic, it's important to read the reviews and summaries. This way, you can get an idea if the story is well - written, follows the characters well, and is in the genre you like. Maybe start by searching for it with relevant tags on fanfic platforms.
There was a young girl alone at home. Knock knock knock. She went to the door but no one was there. Again, knock knock knock. She peeked through the window and saw a shadowy figure. This time when the knock came, the door slowly creaked open. She screamed as a pair of cold hands reached for her.
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.