For an initial orientation on your topic, you can start looking for information in:
- Wikipedia (be critical of its reliability)
- introductory textbooks
- literature reviews
- consulting experts
To assess whether a topic is suitable for a thesis, start searching (online) reference works such as:
- handbooks
- encyclopedia
- scientific dictionaries.
These reference works provide an overview of the perspectives and scientific discussions surrounding a topic. You will find the basic principles and generally accepted knowledge in a particular field, definitions of jargon, references to basic literature and description of intersections with other fields.
Once you have decided on a subject, you can formulate a problem statement, or research question.