Get Query in Panel Field Plugin?

How to access Query data in a plugin?

Could not find this anywhere in the docs.

For example, I wanted to create a simple text or info field in the Panel that displays the emails of all the subscribers to an event (stored as subpages of that page). Ideally I could extend an info or text field, and populate it with the query data

Your best bet is to check out the source code of the pages field:

PHP part: