What are the bounties of the Yonko?
Bounties for Yonkos haven't been shown till now. And IMO, for someone as powerful as a Yonko, bounties doesn't matter much. Bounties are set so that some bounty hunter would be tempted to capture them. But yonkos being one of the most powerful forces in OP, no one would dare to capture a Yonko.

WhiteBeard- Not revealed. 

Shanks- Not revealed.

Big Mam- Not revealed.

Kaido- Not revealed.

Blackbeard- Not given any bounty.