"MN" is neither a recognized abbreviation of any medical specialty, nor of a doctoral degree program.
It is possible that the "doctor" in question intends it as an alternate styling for Doctor of Natural Medicine (Medicine, Natural?). This would be more or less an accepted styling since such "doctors" are essentially self-accredited and not accredited by the same institutions and governing bodies that accredit "regular" doctors, medical schools, and universities.
It could also indicate the doctor in question lives or practices in Minnesota.
It could stand for Doctor of Optometry, or Doctor of Osteopath.
Plastic Surgeon
ddsd
Monetary policy committee
College of Gynaecology
The letters DO after a physician's name stand for Doctor of Osteopathic Medicine.
Master of Physician Assistant Studies
Fellow of the American College of Nutrition
Naturopathic Medical Doctor
it means they work on skin
RN stands for Registered Nurse
Limited Liability Company.