Run a simple adb command from the DOS CMD line
adb connect 192.168.xxx.xxx:5555
adb shell
pm list packages
(xxx.xxx is your watches IP address. Also, be sure to enable ADB debugging on your watch)
You will get an output similar to this
package:com.android.cts.priv.ctsshim
package:com.google.android.ext.services
package:com.android.providers.telephony
The app ID is displayed after package: