"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.
what does the PLC stand for after a Dr.s name
College of Gynaecology
Monetary policy committee
The initials 'MN' stand for Merchant Navy. Likewise, the initials RN stand for Royal Navy.
The letters DO after a physician's name stand for Doctor of Osteopathic Medicine.
Mn stands for manganese
Limited Liability Company.
RN stands for Registered Nurse
Fellow of the American College of Nutrition