You don't have to be in school to study for a doctorate. There are normal doctors and working doctors. A normal doctorate may mean that he has been studying at school. He may graduate from college, then graduate, and then study for a doctorate. The other is a doctor at work. In this case, he usually has already worked, and then he will take the doctoral exam and get his doctorate through self-study. This doesn't always happen at school.

No, generally speaking, the doctoral degree is mainly based on scientific research. Many professional doctors don't need to stay in school all the time, such as forensic medicine. Like medical doctoral students, I usually work in a hospital and participate in clinical work and research. There are also some science and engineering majors that need to do research in scientific research institutes for a long time. They shouldn't stay in school all the time.

You don't have to be in school all the time to study for a doctorate. Some science and engineering students must be in the school laboratory in order to do experiments. If you have a doctor of literature, you can do research anywhere. For example, at home in the provincial library, or go to various places to interview and investigate. Therefore, doctors don't have to be in school.