A good thesis involves the How to start a dissertation. A research question deals with a scientific issue. Therefore, two points should be considered when devising a research question:
A) This question has not been answered due to:
1) not being previously asked
2) being answered in a different way that is challenging.
B) The question has been answered before.
Answering any scientific question requires a prior assumption through which one can find his/her way out. Therefore, the research question should be answered in the previous investigations; otherwise, the research would not have a scientific basis.
The selection of a subject for a master thesis involves the consideration of the need of the community, availability of theoretical and practical research facilities, possession of knowledge and interest in the subject, career prospect, etc. Try not to deviate from the main thesis subject in different sections. Check the background of your research to see if your subject of interest has been investigated previously or not. Choose one of the professors who has the required expertise in the field as a supervisor and share your proposal with him/her.
Note that at least one supervisor or counselor is required to be full-time or part-time and has a vacancy.