Your professor may have listed a topic or provided guidelines about what kind of research to do. That information affects what you decide to research. When professors give topics, they usually give you a general topic. They let you decide what aspect of that topic to research. For example, your professor may tell you to research "children's health." You could choose to research any of the following subtopics:
Connections between school lunches and obesity in school-aged children in Massachusetts
The effect of having siblings on a child's likelihood of developing anxiety
Children's perceptions of their interactions with a pediatrician
anything else you can think of related to children's health.
Your task is to find a subtopic to investigate.
If you are not sure if what you have chosen is acceptable, ask your professor.
Start from Your Own Interests
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.
Generate Your Research Question
Once you have chosen a topic, decide what you want to know about the topic. You will usually write it as a question. For example:
Does providing fruit juice as one of the beverage options at elementary schools in Massachusetts affect the rate of obesity in school-aged children in Massachusetts?
Are children in the U.S. who do not have siblings more likely to develop anxiety by the age of 9 than children who have older siblings?
Does the amount of eye contact a pediatrician makes with their patient affect the child's perception of the pediatrician's friendliness?
You might already have a question you want to know about that topic, but it is fine if you do not.
See what other people have been publishing on that topic or on a similar topic.
The discussion section of a paper usually includes notes about the limitations of the study and ideas for further research. Consider if anything the authors identify interests you.
Use an existing study as a model but change it slightly. Use a different population, method, or outcome. For example, if one study used people in urban settings, study people in rural settings.