How to get the full path to an APK installed in an Android device

Question

I have an app test.aknahs.com.dexapptest called Dex App Test.

1. How can I get the path to the APK on install from a class test.aknahs.com.dexapptest.TestAPKCall,
2. How can I get the path to the APK of the app Dex App Test on install from a class test.aknahs.com.dexapptest.TestAPKCall in another app/ APK

both in an Android device (phones, tablets etc) and in an Emulator.

Thank you all in advance.