Guess what my grandfather said before he kicked the bucket?
Q: Guess what my grandfather said before he kicked the bucket?
A: "I wonder how far I can kick this bucket."
This is a pun based on the American colloquial phrase "kick the bucket". The phrase usually means "to die", but in this case it is to be taken literally. The setup is especially believable because someone's grandpa could reasonably be expected to be dead, and last phrases of deceased people is something that people do talk about.
I like this joke. It is pretty funny.