Answer: knockknock

AnswerCrossword Clue
KNOCKKNOCK

Start of many a corny joke

KNOCKKNOCK

Rap joke

KNOCKKNOCK

Start of a joke

KNOCKKNOCK
Visitor's second attempt
KNOCKKNOCK
Joke starter
KNOCKKNOCKQuestion-answer game of the good old days.
KNOCKKNOCKKind of joke
KNOCKKNOCK1940 cartoon in which Woody Woodpecker debuted
KNOCKKNOCKBeginning of many jokes
KNOCKKNOCKStart of a rap joke?