I believe a notification about a reply to a single, specific post is not available and would be only possible if the person replying hits the "quote" button. Otherwise the forum could not detect it.
But you can watch and mark threads that are interesting for you by subscribing to them. Go to the thread and choose "subscribe to this thread" from the tool bar above (thread tools). Go through and choose your settings (email notification, no notification). You can watch your subscribed threads in an overview in your User CP and see immediately if and who/when somebody posted a new message. Over your User CP you can enter many threads easily and quickly without navigating over many subforums. Try it out, it works well if you are used to it!
BTW, you can also subscribe to whole forums
Thanks Neely for your kind advice