The joke is: - How do you know if someone doesn't own a television? They tell you. The Onion article is just an elaborate version of the joke. The joke here

The joke is: - How do you know if someone doesn't own a television? They tell you. The Onion article is just an elaborate version of the joke. The joke here is people making a big deal about not knowing who Jay-Z is, to the extent they post comments about how they don't know it - rather than just google his name if they were curious. Which indicate that the do know who he is, but want to make a show of being the kind of guy who don't know who someone Jay-Z is.