As a group owner, you can choose to enable notifications for every discussion post that is added to your group page.
From the "Groups" Tab of your Trainer Dashboard, hover your mouse over the image of the group that you want to enable notifications for:
On the edit group view, scroll down to the "Group Settings" header, and you'll see the check box "Do you want admins to receive notifications for any new discussions?":
Check the box if you want to receive notifications, and click "Save Group" to save your changes!