How can one become a professional bodybuilder and still maintain healthy knees?

i.e. best weight and cardio exercises which do not cause damage to the knees.

To be any sort of big guy, body builder or power athlete, you are going to need to squat and deadlift etc., which can potentially damage your knees.

Tough. That’s the way it is.

You can reduce damage and risk vastly though by learning perfect form in your lifts and using knee wraps as your lifting weight starts to get big. Also warm up well and do your stretches!