An exostosis on the outer calvarium rarely, if ever, needs to be removed. They do not affect the inner table, where the brain contacts the skull. Before a surgeon would remove it, he/she would have to have proof that it is actually violating, or has the potential to violate, the inner table. Or, that it is in some way causing actual problems. Otherwise, the risks are just too great for any benefit.
But, if you are adamant about having it removed, most surgeons will want you to have a CT of the skull done for evaluation. And make sure you get a competent surgeon and not someone who says "oh yea I can take that off for you" and has never done it before. The last thing you want is a penetrating injury to the skull or an infection.
Good luck.