as title.

No way at the moment.

Constantly press F5

But IMHO, to be notified that someone had replied to a post (either via email or PM) would be kinda tedious.
Maybe a notification pop-up like that new post in a thread pop-up would be the answer, but still that's a long shot.
This is because imagine if someone had made lots of threads in lots of different sections, the pop-ups would go:
"<someone> had replied to your post in <thread name, click to go to the thread>
"<someone> had replied to your post in <thread name, click to go to the thread>
"<someone> had replied to your post in <thread name, click to go to the thread>
"<someone> had replied to your post in <thread name, click to go to the thread>
"<someone> had replied to your post in <thread name, click to go to the thread>
"<someone> had replied to your post in <thread name, click to go to the thread>
"<someone> had replied to your post in <thread name, click to go to the thread>
"<someone> had replied to your post in <thread name, click to go to the thread>

@fire
reply post not reply topic. reply topic memang can already.

@wkkay
any chance ?

something like the youtube feature would be nice.

Only when a a reply is made through the "reply" button (at the bottom of the post) would such a feature work. Otherwise, if the quick reply is used (as I am now), there's no way to tell whether I'm referring to awh85, EmperorMeng, or firedauz. The semantics just isn't there.

The topic subscription is the next best thing you can use.

yes im talking about clicking reply button (quoting)

then why not putting a checkmark to enable reply notification/subscription to the quick reply?