An instructor posed this question to me, and while I don't think there is a way, I thought it would be worth posting to the Community. You know how email services offer the "receipt" option so that you know someone opened the email you sent? Does something exist within Blackboard that would allow instructors to know that their feedback had been accessed? It's a curious and interesting idea. While one could require students respond to the feedback offered, it is not always worth asking more of the student to ensure you know they read any comments left on an assignment.
I considered that a "Review" button could be added to a module item where students could click as an indication, which is not a terrible alternative.