Listen to Introduction to Knock, Knock, Who's There? online. Introduction to Knock, Knock, Who's There? is an English language song and is sung by The Wiggles. Introduction to Knock, Knock, Who's There?, from the album Whoo Hoo! Wiggly Gremlins!, was released in the year 2003. The duration of the song is 0:06. Download English songs online from JioSaavn.