TMJ specialist. Some dentists specialize in the treatment of TMJ dysfunction. You can start with your dentist, orasl surgeon or orthodontist. It may just be a simple or complex problem depending on your heath and history. Most dental schools have folks who specialize in tmd treatment.
Another dentist. Popping of of the jaw joint is a sign of problems if it occurs before you can open to allow three of your fingers in stack into your mouth. It means that the muscles moving the joint fibrous disc and bone are not pulling in union. The disc is at risk. Many patients by simply opening slowly while watching and dropping straight down can retrain the muscles quickly to not pop the disc. Try it!