Use "Site Feedback" here as an example.
On your thread (hopefully you will see my response in your alerts), there is a "watch thread" link on the upper right. If you go to the top, and click "Site Feedback" you will get the general forum screen.
You should see a "Watch Forum" link on the upper right. If you click on it, it will give you a bunch of options to watch the forum and how to modulate your notifications, including email notifications.
I noticed the "model S forum" has a bunch of subforums first. Then there is a space followed by the Model S forum threads. In this space is the "Watch Forum" link (I almost missed it at first).
Sorry I'm not tech savvy enough to show you diagrams and picture.