When you are interested in a topic, you are more likely to want to learn more about it and to complete your project. Think about what interests you. You might simply be curious about something or you might have experienced or witnessed something that makes you want to know more. For example, you might be fascinated by airplanes and want to do research on something related to airplanes. Or, you or someone you know might have a disease that you want to know more about.
If you are stuck, try looking at recent articles in journals for your discipline, checking social media, or skimming newspapers. Eventually, you should find something that excites you.