I've gotten to grade 8 in the drums and I want to know how many more grades are left for me to finish.
The system of exams for schoolkids ends at Grade 8. If you really want more exams, there are various diplomas and degrees. But mostly people just go out and do it. The job requires musicianship and experience even more, perhaps, than technique. I make my living partly from playing piano, but can't remember when I was last required to play anything 'difficult'.