That depends on the local environment and how close the population is to a local fitness maximum. The closer the population is to the fitness maximum the less chance it will have a mutation to increase fitness - if you’re near the top of the mountain already there are few ways to climb higher. However in the real world environments are constantly changing and reproductive fitness maxima are always moving. The process of evolution allows the population to constantly track and move toward the local fitness maximum. Asking for a specific number of beneficial mutations is rather silly as there are way too many variables in the equations to calculate.
3 Likes