Open command shell.
adb devices
That will desplay the connected device ID, e.g.: 28a890fd
Next, open adb shell and get details of the currently opened app:
adb shell
dumpsys window windows | grep -E ‘mCurrentFocus’
If Google Play is currently opened, you will get the appPackage/appActivity details, e.g.:
com.android.vending/com.android.vending.AssetBrowserActivity