To find the oldest joke you have to go way back to 1900 BC. there the Sumerians which would now be where southern Iraq. The appearance of the old style jokes appear to be that of mischievousness and out of norm activities.
Firstly though here is the second oldest joke told by King Snorfu about a pharaoh in 1600 BC "How do you entertain a bored pharaoh? You sail a boatload of young women dressed only in fishing nets down the Nile and urge the pharaoh to go catch a fish."
the oldest Brittish joke was - "What hangs at a man's thigh and wants to poke the hole that it's often poked before? Answer: A key."
The oldest joke in the world is -
"Something which has never occurred since time immemorial; a young woman did not fart in her husband's lap."
Ladies! you all used to fart on men's laps apparently.