There are a ton of resources online that offer many of the sample questions that are asked during a Peace Corps interview. The process may have changed since 2014 when I interviewed but the questions were primarily focused on my motivation to serve, skillset and experiences, cultural sensitivity and adaptability, and collaboration style. The interview skills you have gained by graduate school should be enough to maneuver through the interview well. The main components will be articulating your passion and purpose and how they will enable you to be a good volunteer for your community.
From discussions with other Peace Corps volunteers, the interview process for us were widely different. My interview was 2 hours to the minute and there was no rapport built during the conversation. I sat down and she never looked at me, she simply asked me the questions and typed my answers on the screen. Just about all of the other volunteers I spoke with had very causal, warm conversations and their interviews were not more than half an hour. From what I hear, you can generally be confident in having the latter interview style.
They did not specifically ask me health related questions during my interview. At the very end, she indicated that I had the skills to be a health, education, and youth development volunteer and asked which I wanted to do. I chose health volunteer which Peace Corps changed to community health advisor while I was serving.
The main takeaways would be to think about how your values align with the Peace Corps pillars and if you feel like you can adapt to the needs of your community to do meaningful and beneficial work alongside your community partners. If you can thoughtfully articulate your why and how in terms of this mission, you will be prepared for the Peace Corps interview. And of course, don't be shy to ask any questions that you have. Peace Corps is a commitment and you want to make sure you know what you're getting into.