Locating application files on the android system
Using abd shell and the ps command, I determine the name of the package of the application.

Then, the files related to an application are located in the directory:

/data/data/package.name/


But the files in here are not accessible unless you have root rights. Or unless you run adb shell, and run-as my.debugable.app.
Unfortunaly release application are NOT eligible for the run-as command.

Not possible to list files in such a directory with ls

So the necessary next step is to learn how to root an android phone.