i have searched all over to figure it out and to find an answer but i can not find one does anyone know? thanks

The highest earning, as far as I know is the Director of SAI (SAI). 30K per day. But you need really high INT to get the job in the first place and even higher to get promoted to the highest job level. 500 Int to start and 1600 for the top position.

You can check out this Job Agency Guide and Discussion, its not completely up-to-date, but its still pretty relevant.