Pending legislation or regulations are good sources to find timely issues to write about.
Topics can also arise from your daily activities like a case or statute discussed in class, or at your workplace. Your professors can also be an asset in both identifying and helping you refine your topic. If you have an interest in a particular area of law, seek out an expert on the subject and discuss it with them. Their experience in a subject field is invaluable and can never be replaced by Google or some other database search.