When you don't know anything about a person, you have a conversation with them by asking them things:

How many people work for you?

 

How long have you been in the police force?

 

What is it like being a police chief? What is the best thing about your job?

Or if you prefer, you can ask more personal questions:

Do you live near here?

 

I visited X recently, have you ever been there?

 

This [item being eaten or drunk] is really good. How is yours?

If you feel that questions are "nosy" then try telling the person you're impressed by them.

Wow, Chief of Police, that is impressive, I was not expecting to meet such an important person tonight.

Or that they know things you don't

I really don't know anything about [your area] but I'm interested in it. What can you tell me about it?

A senior person can naturally expect to carry most of the burden of conversation with a younger person. You can give a little prompt that should get the impressive person to talk quite a lot, and you can listen attentively and say "oh really? that's fascinating" and such from time to time. Of course, this particular person might not be a "big talker" or might be tired from a long day and not feel like talking. But questions and prompts generally work to get the senior person to talk, letting the junior person relax a little and just listen. That should also leave you feeling less nervous.

When you don't know anything about a person, you have a conversation with them by asking them things:

How many people work for you?

How long have you been in the police force?

What is it like being a police chief? What is the best thing about your job?

Or if you prefer, you can ask more personal questions:

Do you live near here?

I visited X recently, have you ever been there?

This [item being eaten or drunk] is really good. How is yours?

If you feel that questions are "nosy" then try telling the person you're impressed by them.

Wow, Chief of Police, that is impressive, I was not expecting to meet such an important person tonight.

Or that they know things you don't

I really don't know anything about [your area] but I'm interested in it. What can you tell me about it?

A senior person can naturally expect to carry most of the burden of conversation with a younger person. You can give a little prompt that should get the impressive person to talk quite a lot, and you can listen attentively and say "oh really? that's fascinating" and such from time to time. Of course, this particular person might not be a "big talker" or might be tired from a long day and not feel like talking. But questions and prompts generally work to get the senior person to talk, letting the junior person relax a little and just listen. That should also leave you feeling less nervous.