GJ has email notifications built in. The user needs to navigate to the group then click the Notifications menu item for that group. From there they can configure various notifications to be sent. In GJ configuration you can configure the defaults for notifications in addition to if you want them to be emails or PMs.
If you mean activity like with CB Activity you need to install CB Activity, GJ, and CB Auto Actions. Once done ensure all 3 are published then within CB Auto Actions > System Actions ensure the GJ activity you want to log has its action published.