I think in the US, general medical education spends a day or two on diabetes. Jeez. No wonder we walk into the office a GP and find they don't know much about diabetes. I finally sought the advice of an endo when it became clear that my GP was not competent to treat me further. She absolutely refused to prescribe insulin and finally when I requested the antibody tests and a c-peptide to determine whether I was T1, she said she didn't know how to interpret them and that I couldn't be T1 since T1 was only diagnosed when you ended up in the ER with DKA. Jeez.
I have diabetes, I have T2, but like all of us I live with it everyday. Over time, I will have a pretty darn foundation of knowledge about diabetes. And I now clearly know when a doctor is competent. But there is another side to what I want out of a doctor. I want not only a doctor that is knowledgable, I want one who listens and lets me make decisions about my care. At one point I had to leave an endo who was quite knowledgeable, but he didn't listen or involve me in my own care. And I have had doctors who, even if they were not diabetes experts, they listened, gave me my prescriptions and really helped.
You can read more about my experience looking for a new endo here.