My first question is how do you keep me out of pain? Is there sedation?
Then I would ask normal questions, like what type of testing do you do to see if the materials you use are compatible with my body?
I found these on the internet:
Are you mercury SAFE or mercury FREE in your office?
What are your procedures for removing mercury fillings?
What alternatives to root canals do you offer?
Do you avoid the use of fluoride?
Do you use digital x-rays instead of film?
Do you offer alternatives to metal implants?
Do you offer ozone treatments?
Do you have a CT scanner for checking out the health of my root canal teeth, or to see if my jawbone is strong enough for an implant?
Does your office offer alternatives to antibiotics or nontoxic alternatives to pain medication?
Does your office offer alternatives to drill-based cavity treatment?
Oh I found this site with good questions also: /iaomt.org/for-patients/questions-for-your-dentist/