Did you ever figure this out? I’m stuck here now as well.
I found a possible fix, though it isn’t what the book says.
Do this:
Build -> Clean Project
Build -> Rebuild Project
The path to the R.java file then should be in the directory
app/build/generated/not_namespaced_r_class_sources/debug/processDebugResources/r/com/bignerdranch/android/geoquiz
I really don’t know if this is the fix to this, I found it here: No R.Java (purchased book)
But even on that post someone implies that this shouldn’t be how our app is and there is possibly an error.
If and when I found a solution, I will let you know!