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

Jokes

 * The Doctor is only late when he travels in his TARDY-IS.
 * The TARDIS's tea-making machine only serves English breakfast tea because the Chamomile-ean circuit is broken.
 * A Dalek tells a petrol pump to take its finger out of his ear while he exterminates it.
 * Drahvins are the best at steering a car.
 * Magnets find Daleks attractive.
 * The Doctor's TARDIS is stolen by pirates.
 * The First Doctor and Susan land somewhere that has a yellow sky.
 * The best place to get a sandwich on Skaro is Dalek-atessen.
 * A galley fray is when two Time Lords fight in a kitchen.
 * Telos has a big tomb full of Cybermen.
 * The Second Doctor and Jamie go to a moonbase, where Jamie can jump higher than a lamp post. The Doctor says that lamp posts cannot jump.
 * The Macra's favourite card game is Snap.
 * The rockets that invented the Transmat all fired.
 * The Yeti enjoyed the low gravity when the Great Intelligence sent them to the moon. They were woolly jumpers.
 * Freeze a Jolly Good Fellow is sung on an Ice Warrior's birthday.
 * Ice Warriors put Mars-malade on their toast.
 * The Fish people blushed because the sea weed.
 * The Doctor is from from Gallifrey. Which part? All of him.
 * ...timing! The secret of Gallifreyan comedy is...
 * Autons never need their batteries changed because they Auton, and on, and on, and on.
 * UNIT keep their armies up their sleevies.
 * The Third Doctor drives Bessie along the M4. The Brigadeir warns him to be careful as there is a madman on that road driving the wrong way. The Doctor exclaims that there are hundreds of people driving the wrong way.
 * Silurians weigh themselves on the scales.
 * The Doctor has not defeated the Chronovore yet because it is very time-consuming.
 * UNIT are investigating reports of a spaceship shaped like two rashers of bacon, a Cumberland sausage and an egg. They ask for witnesses to come forward with an information about the Unidentified Frying Object.
 * The Silurians have fantastic gardens in their underground cities because they have green fingers.
 * The Master tells the Doctor that they are not so different because they both have the same first name ("The").
 * The Sea Devils dare not fight shellfish because of their big mussels.
 * The invisible humanoids of Spiridon are terrible liars because you can see right through them.

more to come

Continuity

 * Yaz encounters a Judoon. (TV: Fugitive of the Judoon)
 * The oldest joke in the universe is the same as the oldest question in the universe. (TV: The Wedding of River Song, The Name of the Doctor)