A new doctor usually does not have a clear research focus as it demands in-depth subjects knowledge to develops correct research questions.
Your thesis guide usually has adequate experience. So concentrate on the following points
Field of work of thesis guide: The outcome of a well-executive research project provided answers to a particular research question. Besides, it increases the understanding of that specific topic, which in turn help in raising many other research questions, which finally becomes bases for further research.
For example,
A cross-sectional study designed to identify risk factors for a disease x in a population. The outcome of the study is the identification of A, B, and C as risk factors for the disease X. It also gives rise to a question as to what extent the presence of the risk factor A in the population increases the odds of having the disease X. , a second study (case-control) is required to answer this question.
The previous experience with the research in the same or similar topic also gives one the idea of the difficulty faced in the study planning and execution.
You can get an idea of the field of your guides interest by looking at his/her previous publication or thesis supervised.it will provide you with an excellent sense of the focus and direction of the research interest. It is better to find some topic in alignment with the guides research focus and direction.