How to track pop-ups using google tag manager events?
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
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