To do this, first you will need to obtain the URL from the Video.

Navigate to:
  1. onMessage > Content > Videos
  2. Click into the Video Category that the Video is in
  3. Click the URL Button to display the URL of the Video
  4. Copy the end of the Video URL so ?#Video/12345

Then find the Public page you want to overlay the video on (to display as a pop up on that page)

for example: http://www.schoolname.org/page/Page Name/PageName2
Then you will add the Video URL to the Page name so it should look something like http://www.schoolname.org/page/Page Name/PageName2?#Video/12345 This way the Video will display as a pop up overlay on that page. 

Then you can use the URL to insert in pushpages etc.