RE: How to show opportunity sub grid fields on opportunity System view
Hi,
It seems that you wish to show the fields of the Feedback entity that has the N:1 relationship with Opportunity entity.
It is not logically possible to show the fields of a related entity having N:1 relationship with the parent entity as there may be multiple child/related records of the Feedback for a single Opportunity record so it becomes very much confusing that which Feedback's values would be shown.
Alternatively, if you would have tried to show the Opportunity values on Feedback view then it was pretty simpler :).
Hope it helps!