Based on the new stable release of Android Studio (3.6) we have:
So, now to find your generated resource classes you need the following steps:
1) Open your project.
2) Go to your module build path.
3) Open the outputs/apk/debug/app-name-debug.apk file.
4) Choose your classes.dex file.
5) Look at the down placed area and go to your full package path.
6) You can see all bytecoded resource classes. So, scroll down to what you are looking for.
7) Expand the resource class you need to proceed (for example, let it be R.id)
8) Go to you id's.
That's it.
UPDATE:
If you would like to see actual id integer number you should follows steps below:
1) By (7) Go to the resource class you need to proceed and right click to show the context menu
2) Choose "Show Bytecode" to see the flexible dialog "DEX Byte Code for R$id", for example, for id class
3) Scroll down to the actual id to look its number
