Someone replying to your comment doesn’t change your karma points. Someone upvoting your comment may probably increase your karma points (the may probably is because of the undisclosed algorithms that attempt to compensate for gaming the system).

In other words, looking at karma won’t tell you whether someone replied to your comments or not. There is nothing on HN to indicate replies unless you dig into your comments history. There nay be other sites or browser extensions that could help on getting notified.