I don't know the joke, could you explain? Googling it didn't give me any hints (the top result is an article at The Onion "Area Man Constantly Mentioning He Doesn't Own A Television")
- 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.
