Facebook groups has got some cool new features, including you can now subscribe to a facebook group post conversation updates, so that you get notified in case someone comments on the entry conversation you have subscribed yourself.
Follow the procedure below to subscribe to facebook updates for a specific entry for facebook group
1. Login to facebook.com
2. Go to facebook group page and click subscribe for a particular facebook post entry to receive notifications as shown in the image below.
3. Once you are subscribed to this facebook group entry post, you will receive notifications if some one comments on the same post that facebook group.