One source for a sense of early medieval humour is the Anglo-Saxon Riddles, some of which have bawdy and humourous meanings and all of which are meant to entertain the listener.

They take a "joke-like" form to the extent that they offer a brief enigmatic description (compare: "what's black and white and read all over?"), for which the listener is meant to guess a meaning which serves to entertain. They differ, structurally, from most contemporary jokes in that the subject of the joke is generally the personified speaker (i.e., "I am [x], [y] and [z]" rather than "what is [x], [y] and [z]?").

Here is a past thread on Medieval humor, with answers that include Late Medieval and Early Modern jokes.