In some cases, such as for a course assignment or a research project you're working on with a faculty mentor, your research question will be determined by your professor. If that's the case, you can move on to the next step. Otherwise, you may need to explore questions on your own.
A few suggestions:
Choose a topic that interests you! You'll be spending a lot of time with it.
Explore your topic using your textbooks, reference books, and articles and by consulting your professor.
Be open to tweaking your research question as you gather more information.