You can
export the entire Blizzard UI code from the game and look for the template there.
Addons can have their own templates so you need to make sure the code you're looking at isn't using one of those (unless you have the addon installed).
Also, frames/templates can change over time (like become an intrinsic or another template entirely or just plain removed) so you also need to make sure the code is current and for the correct game client (vanilla/retail/latest classic)