or the waite? When someone waste a lot food in buffet, should the manager talk to the customer or the waite?
Can someone tell me why and why not please?
I mean should the waite or the manager talk to the customer and tell them not to waste so many food.

Well, it's certainly not the waiter's fault. And actually, wasted food is quite common (extremely common) for buffet style restaurants. Have you ever tried to clean up one of those places at night? Seriously a mess.