For tracking every time a pop up appears on your site,  push an event within data Layer and set up trigger using that event

//implement this code when popup appears

dataLayer.push({

   'event’:'popup'

});

Then set up a tag that triggers on custom event i.e popup. You can use the same approach for other user actions including implementing code on popup form submit.

see the original question: https://productforums.google.com/forum/#!topic/tag-manager/BeCq3MrP6Mw;context-place=forum/tag-manager