Some key commands:

adb shell pm list packages
adb shell pm path <package from above>
adb pull <path from above> <local path to download to>

Here’s an example applied to Neko Atsume, the premier internet cat game:

C:\Users\chris>adb shell pm list packages | grep neko

C:\Users\chris>adb shell pm path

C:\Users\chris>adb pull /data/app/ nekoatsume.apk
/data/app/ 1 file pulled. 14.1 MB/s (19756023 bytes in 1.341s)

Happy Hacking 😺