If anyone works in club as a waiter. He just serves and get payment of that. Regardless club earnings are haram like selling beers, gambling etc.
But the one is getting payment for his services, is it matter that what’s the source of that payment?
First of all, It's haraam to sell Haraam things. and what you earn from that is haraam too.
Second, if you are sure (100%) that somebody gives you from haraam money. but if you are not sure and have doubt you should assume it's not harram.
Aside from harram things that may happen to him/her by working there, the money they give him/her is harram.
(Rumi in his book, Fihi Ma Fihi, has a story about the effect of eating things from bad people and who they can effect good peoples)