Answer: knockknock

AnswerCrossword Clue
KNOCKKNOCKStart of many a corny joke
KNOCKKNOCKRap joke
KNOCKKNOCKStart of a joke
KNOCKKNOCKVisitor's second attempt
KNOCKKNOCKJoke 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?