Let's say that a clergyman (rabbi, priest, pastor, minister, bishop, whatever) buys a lottery ticket. He wins $750 million. Should he keep it or donate it to his church or synagogue?

Clergy men and women are people too. I do not think they have any obligation.
I however would be wary of where their gambling money is coming from.

If they take a vow of poverty they might turn it all over to the church, but I think most clergy can do whatever their conscience tells them.

Clergy for many is a job.

There is a Jewish joke where a rabbi pleads with God to let him win the lottery. He pleads over and over but he just doesn’t win.

Finally an exasperated God says, “Shlomo! Meet me half way! Buy a ticket!

Priests take a vow of poverty, although I would guess that many or most are not poor, because congregants give them gifts of cash, invite them over, etc.

Ministers and pastors are whatever they are. Some wealthy examples are Joel Osteen and Billy Graham.