This is the third menu item that appears under WP Travel option.
To enable the enquiry feature you have to enable this by going to Admin Panel > WP Travel > Settings > Misc. Options.
The Enquiries section under the Coupons section in the dashboard menu list all the enquiries that are made from the front-end Trip Inquiry section.
The Admin will be able to edit the content of each individual enquiry by going to individual enquiry edit screen.
You can even manage the template of the enquiry from WP Travel > Settings > Emails > Enquiry Email Template.