The following is from the ECUAD Writing Center Handout: Writing a Research Question.
A research question is a clear, focused, concise, complex and arguable question that will lay the groundwork for a thesis by offering a focus for your exploration of a topic that interests you. Although a strong research question is a good place to start your thesis, you should be prepared for it to change as you carry out primary and secondary research.
The following steps are merely a guideline for the very beginning of the process of writing a research question. You might not follow them in exact order and you might return to or move between them at different points in your research process.
None of these are absolute rules (except, perhaps, the first and the last), but rather goals to reach toward through the process of writing and revising your research question.