I know it has been a little while since this post but I have had two PHN interviews (in Virginia) the second one was just today so I thought I would answer.
The interviews were similar, 2-3 panelist reading questions from a list that both you and the interviewers have a copy of. Then they write down your answers, so making eye contact was difficult. The first section of questions are background/definition/philosophy types of questions. Such as: how do you define public health? what is a public health nurse to you? what are some public health challenges in this community and how would you address it? Then there is a section of scenario questions. The scenario questions are clinical and often have to do with priority setting. For example, "you walk into work and A, B, C, and D is happening. What would you do, in what order, and why".
I noticed that both of the interviews asked very little about my background or current position.