what is the process for choosing a research topic? what makes a good research topic?

The most important thing is a good "Research Question".

Pick a topic you like or need (if the research have to be done oriented to any especific subject).

After having a general topic/subject, ask yourself some things about that topic. Think what are the known things about you topic, what are the unknown things about it.

Then, pick some questions on your subject and ask yourself "Why is it important to get an answer for that questions?" Answering that kind of questions will reinforce the need of answers and that's what justify the research topic.

A good research topic is usually unknown or not deeply known, although there are some known topics with unknown details or unfinished research (partially researched topics).

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There are several publications on "Research methodology" that can help you on the research subject picking process and the research process. See link below.

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"Developing the research proposal" (2nd link) shows some interesting info on research.