What is the correct title for a student that has submitted his thesis, and is waiting for the defence?
Some people will say it's ABD (All but dissertation). It's stupid and meaningless, you either have the title or you do not.
The simple truth is "nothing", you simply don't use any doctor title. If you need to specify anything in the CV, say "expected to defend in August 2016" (or whatever the date is); this is the information people need: you're realistically defending soon, they know when exactly your studies end and when you're free to be employed or whatever.