Knock! Knock! Who's There? (novel)

 was a book published by BBC Children's Books. It contains jokes and short comedic stories. It has a narrative-based framing device in which the Thirteenth Doctor and Yasmin Khan have somehow been trapped inside of a joke book, and are trying to find a way out.

Publisher's summary
-What do we want?

-TIME TRAVEL!

-When do we want it?

-THAT'S IRRELEVANT!

Packed with a dimensionally transcendent TARDIS-load amount of jokes, gags and riddles, this is the official Doctor Who joke book! Remember: it's funnier on the inside!

Synopsis
This books narrative framing device is told through a series of short knock-knock jokes interspersed throughout the book between the Thirteenth Doctor and Yasmin Khan.

Yaz asks the Doctor where they are, who claims that they have been trapped in a joke book. When asked why, the Doctor suspects that it has something to do with that chicken crossing the road. The Doctor goes on to explain that chickens are mysterious, and that there's something suspicious about their eyes. Yaz questions when they became trapped, with the Doctor suspecting it was when they followed a Silurian, and Judoon, and a Hath into a bar, and they all started arguing over how to change a light bulb. Yaz asks the Doctor how they are going to escape, and the Doctor informs her that they need to find the first joke, the oldest joke in the universe, hidden in plain sight. They find the joke:

''Knock! Knock!''

Who's there?

Doctor!

''Doctor? Doctor Wh...''

Contents

 * Doctor Who jokes