Your research idea needs to be fresh, relevant, and interesting. Read as much as you can on your topic. Look at textbooks, read journal articles, watch relevant documentaries, and talk to people in the field.
From that, make lists of ideas and possibilities and research those. Take a deep dive down multiple pathways. Get as much information as you can. Take notes and keep track of them, either in files on your computer, or take them in a notebook.
How do you know when you've found what you're looking for? When you come up with a question that won't go away. When you can't stop thinking about an idea. When your wonder on the topic keeps you up at night.
I know that we're both posting on a 6 year old thread but what you say is true.
My problem is that someone who is working on a Masters Thesis has already had a shedload of schooling and have presumably been taught how to do research. The OP said "But I have not a clear idea what research can be done". Isn't developing such a "clear idea" of what research can be done supposed to be a part of the discovery process and isn't the process of how to develop such a hypothesis taught in Masters level education?
To be more blunt, isn't asking the general public how to figure out what research should be done to support a chosen topic for a Masters Thesis gaming the system a wee bit?
--Jeff Moden
Change is inevitable... Change for the better is not.