How to see the reply would depend on how the user replied.

If they received an email and replied to that, then their response would be received at the Reply Email set up in the email notifications for the note type.

If the user responds to the official note within the App, the reply will be received in the original sender's Official Notes Inbox. The number will turn red to indicate an unread note User-added image

The Official Note the user replied to will be highlighted in blue.
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Official Note replies can also be viewed on the Candidate's Admissions Profile.
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