You will see a blue circle and a number inside it on the top right corner of the screen. Click on it. If the number appears next to "Opinions", click on that. Then on " Opinions Comments". Finally, the first question on the list.
It'll notify you when someone comments on your response. If you comment on another user's post and they reply, it will not notify you, however, but you may check these via the "Opinions Comments" section.