There are endless possibilities in the field of Abnormal Psychology research. The goal of scientific research (in any field) is to use your interests, creativity, and innovation to pose NEW questions for exploration. Even within areas of research that may have "already been covered" there are often hidden gems inside those research findings.
First, I encourage you to narrow your focus when it comes to abnormal/developmental psychology. Is it learning disabilities? Is it forensic psychology? Is it developmental issues on the autism spectrum? Is it genetic disorders? etc.
Next, I encourage you to use Google Scholar to find published research papers of interest to you.* Read through them and you will find that at the end of each research paper, the authors will pose questions for additional research and/or suggest other factors that should have been considered when constructing the original experiment. Adding a new factor to a pre-existing study and examining the change (if any) in the results creates new research in and of itself. It will spark your own scientific inquiry and show you how unlimited the possibilities are. I hope this helps!
*Be careful, Google Scholar publishes some papers in full at no cost to you, but some require memberships in certain organizations or a one-time purchasing fee. I don't advocate that you pay for any research papers on Google Scholar. Just keep searching and eventually you'll find a bunch of free research.