Pop-Up notification is enabled from the DNNForge - Message Count module. In most installations this is simply called "Messages" and looks as follows.



To enable Pop-Up notification hover over the blue arrow next to the module name and select "View Options"



Once in the options screen put a check mark in the "Use Popup" box and select the color of the Popup you wish to use.



Click on "Update" and your finished. The next time your users log in and land on a page that has a "Message Count" module configured as above they will receive a Pop-Up in the lower right of their screen indicating they have a private message.



Clicking on the Pop-Up will take them to their inbox.