Ahh, again, missunderstanding what you wanted :tear:...
You can add a forum to your watchlist from the "Forum Options" dropdown on the forum display page (the dropdown can be found to the right of the "New Topic" button)
You can view, and edit, your "watchlist" from "My Stuff" -> "My Watchlists".
And you can turn on "Email Notifications" for items individually from the "My Watchlists" page by clicking on "Edit Watched Forums" (from the Watched Forums tab ofcoarse).