Android: .obb files location

.obb files are APK Expansion files.

Before Android 4.2:
/mnt/sdcard/Android/obb/<package-name>/

Android 4.2 and after:
/mnt/shell/emulated/obb/<package-name>/

If you have root access:
/data/media/obb/<package-name>/


Ref:
How do I install a .OBB on 4.2 jellybean without rooting? - xda-developers