To find the path of existing applications in the DEP settings screen, you need to access the Windows Registry (regedit) of the computer:
Navigate to the following key:
In here you should be able to see the paths of all the applications already added.
Sometimes you cannot see a mapped drive in the normal DEP setting screen, so you can add it directly in the registry. Also see Making Drives visible for DEP Settings Windows 10
Right click and select NEW STRING VALUE. Type the entire path in the Name and type DisableNXShowUI in the Value Data field. The path you want to add is the exact path for set in the shortcut you use to start the software.
Please note that you should ONLY do DEP settings on computers that have been found to require it, ie, they are getting the Fatal Error Application Has Stopped Working message with the error exception code Cx0000005.
The exception code can be checked in the Event Viewer of Windows, if the error pop up does not show it. Doing this setting on computers that are not getting the error will have the opposite effect.