Personally I wouldn’t ask if I get 40, 50 or 60% of the pie.
Id try to make the pie larger, or make more pies- if that makes sense for this question. Personal trainers work with their gyms in a mutually beneficial relationship. If one side doesn’t hold up their side, everyone gets a smaller paycheck.
70% of being a personal trainer is selling yourself. Do that, present good classes and the money will make itself.