To see whether or not a client has viewed the itinerary or proposal you've sent them, go into the trip in question and click the blue "Send" button at the top right of the page. Hover over their name and the status will be displayed.
To see if a client has Viewed, Opened, or Responded to a Form, navigate to that client inside the "Contacts" section and click on "Forms".
If your clients are having trouble locating what you've sent them through Travefy, you can try the suggestions outlined here. https://intercom.help/travefy/en/articles/4986644-why-are-my-travelers-not-receiving-their-trip-invitations.