Does the popup appear after an event? E.g. Is it after you click a button? Or after something loads?
If it's after a button click, then you can probably tie it to an event listener on the button click. For example, if the button has an id of #btn, then the code would be something like this in between the document.ready method:
$("#btn").on("click",function(){
$('.DashboardPanel__ProductTypeTitle').prepend("About |");
});
Our Canvas instance isn't using the catalog so I can't give you specific classes or IDs. But what this is basically doing is that if the button with id #btn is clicked, then it will run the prepend code on the .DashboardPanel__ProductTypeTitle class.
Since the JS Override file runs after all other JavaScript, when your code runs to prepend some text, it should run after the popup element is created. You just have to find either the class or ID associated with the event responsible for generating the popup.
Click is just one type of event. You can find info on other event types you can listen for here: https://api.jquery.com/category/events/