Best practice when searching for users with surveys?

Could you suggest best practices when performing a user search with surveys with open questions?

The context a web page has (unexpectedly) a lot of visitors we do not know anything about. This page does not appear in the navigation and no SEO effort has been made to improve its ranking in the search engines. The subject of the page is a common subject also for other pages.

We wondered why this page has so many visitors. One idea was to ask a single open question in a survey to find out what visitors are looking for. The survey will be integrated on the page (as a widget) or will be displayed as a popup. Exact implementation remains to be determined. Is there any best practice you can suggest for this scenario?