My tooth had a root canal and crown replacemtn that keeps getting dacayed. Do I need an oral surgeon or endodontist?

Your dentist. Contrary to what some people believe, a root canal treated tooth with a crown place on afterwards can still develop decay. You still have to maintain proper oral hygiene with the tooth as you would with any other tooth. This also means regular dental check ups. Have your general dentist evaluate the tooth to determine what course of treatment is indicated.
Ask your dentist.. I am not sure of the exact cause of the problem. Do you normally have issues with decay in other teeth as well? It may be an issue dealing with your care. Perhaps the dentist has difficulty with this tooth for some reason; is it a compromised situation, is the dentist not doing his/her job well? Perhaps you would benefit from a second opinion and a fresh set of eyes. I would see a dentist.
No. You need a grade triple a dentist. And I am concerned anytime there is repeated infection. Does your doctor know about this?Why not?
General dentist. I am concerned about why you get recurrent decay on the same tooth. If this is not a hygiene problem, then i wonder if all the original decay was removed when or before the root canal was performed. If the tooth has a crown, have your dentist remove it, remove all fillings, remove all decay, and eval if there ie enough left to restore. If so, a buildup and new crown will be placed.
A general dentist. You should first see a general dentist to determine what the problem is and its cause. Based on those finding, the dentist will decide whether or not you need specialty care.
Not yet. You should see your general dentist first to examine the tooth to see what's going on. He/she will refer you to a specialist if they think that's in your best interest; however, decay under a crown does not necessarily mean you need the tooth pulled or the root canal treatment re-done.