Everyone can’t write on every topic. One has to have a niche that one enjoys reading and writing about.
You let the interviewer drill down to ask you questions about your niche. It is your expertise. So make sure you drive the next question for your interviewer than to let them keep on grilling you on the topic they know the best.
As an example, if you are a food enthusiast, you will love writing about food. You won’t enjoy the automobile niche.
As a writer, choose your area of interest and let the interviewer know your area of interest and expertise.