This issue could use a response from the team. Currently I have to keep my email notifications around just for the link to the comment, so that I can respond at a later point.
Edit: At the risk of blurring the original request, I’m referring to comments on notebooks that I’m subscribed to (i.e., have actively subscribed to or commented on at least once). Since there is no explicit reply mechanic (yet?), having these comments in the activity feed is essential to keep track of conversations on other notebooks.