Do a Windows search for ".prtl".
But do note that the title templates for Premiere Elements will be in a couple of places.
The titles that are installed with the program will be in Program Files/Adobe/Adobe Premiere Elements 2019/Rich Title Templates\All_Lang while titles that are downloaded with you select them are in ProgramData/Adobe/Premiere Elements/17.0/Online/Rich Title Templates/All_Lang.
So it kind of depends on what you're looking for.
These are titles (.prtl) created and numbered
by: Text> New Text> Default Text> Title 01 to Title 60; all viewed in Project Assets and placed on Timeline.
Unable to find the Titles in Program Files/Adobe.. and ProgramData/Adobe..
Premiere Elements does not save your titles as individual files, HBO. They're just part of your project (.prel) file.