Knock-knock joke

~noun

Entry: one of a class of childish jokes told as a dialog and usually including a pun; in the following form:

"Knock knock."

"Who's there?"

(The teller of the joke says a name).

(The person to whom the joke isn't being told repeats the name, followed by "Who?")

(The teller of the joke says a pun based on the name).