Where is stored my system APK ?

Given a package name of a system app, how can I get its APK path ?
First, connect your device and from the platform-tools, and do a :

adb shell dumpsys > dumpsys.txt

Now, you can edit the file dumpsys.txt with your favorite editor and search for the following string :
Package [<YOUR_PACKAGE_NAME>]

For example : with the package name com.google.android.setupwizard
you’ll have :

 Package [com.google.android.setupwizard] (bf142e1):
    userId=10018 gids=[3003]
    pkg=Package{33203806 com.google.android.setupwizard}
    codePath=/system/priv-app/SetupWizard
    ...

You see that codePath is interesting here. You can now easily navigate to thiscodePath to get the name of the APK , by listing the files available :

$ adb shell
$ cd /system/priv-app/SetupWizard
$ ls 
SetupWizard.apk
arm64

To backup this APK, you can now simply run the following :

adb pull /system/priv-app/SetupWizard/SetupWizard.apk SetupWizard-backup.apk