You disabled notifications, but want to get activity updates on activity for a specific post?
You enabled notifications, but don't want to follow a particular post?
To disable or enable notifications for a specific post, all you have to do is:
Find the post in the newsfeed, by clicking on the "News" tab located in the menu column on the left
Click on the three-dot button at the top right corner of the post
Click "Activate notifications" to receive updates for this post or "Deactivate notifications" to stop getting them