The first place to look for a topic is within the assignment itself. In short, you will choose a piece of literature and an element within the work to write about. Your topic needs to be sufficiently narrow or broad to be able to research and write about. Appropriate topic selection can set you up for success if done well.
Choosing takes research!
In order to get a good start at choosing a topic, you need to do some background research. Simply saying "I'll write about The Strange Case of Dr. Jekyll and Mr. Hyde" is a good start, but isn't going to get you anywhere useful. By doing background research, you can find additional terms, concepts, and ideas to turn a general idea into something that is easier to research, such as the role of addiction in The Strange Case of Dr. Jekyll and Mr. Hyde.