Here are a couple of these 1969 Topps Bubblegum TV Knock-Knocks Cards. Artist and writer uncredited, as was the usual case. These are some awful punning old knock-knock jokes, which always make me groan and smile simultaneously. Although these were out in 1969, I have only recently learned of their existence.
It looks like there may have been a couple of versions of these cards, with one set titled "Knock-Knocks" and another "T.V. Knock-Knocks," as well as a series number beneath.