This isn't particular to CUNY, but I also had a 30-minute interview for another History PhD program. Because 30 minutes is so little time, I think they are mostly interested in your work. I overprepared by trying to know about all the work my POI had published and was ready to list out all the aspects of the program that I felt fit me. Instead, I was mainly asked to expand on my previous historical research (mainly my master's dissertation). I was also asked about methodologies and what I expected to do with my research at the PhD level, as in what about the topic interested me and how I would expand on it. Again, 30 minutes is actually very little time, and they are probably trying to stick to a schedule. I would suggest revisiting your previous work and practicing responses to summarize it as best as possible. This might not be the experience for everyone, but my interview was very specific to my particular historical topic and not much about the program itself. You can obviously demonstrate your knowledge of the program by asking questions yourself at the end. Hope this helps & Best of Luck!