We've recently updated our WHD to 12.3.0 and I've been trying to find this out for the last day, but the lack of information is making me think that the feature just simply isn't present. When you link tickets together using the Problem/Incident relationship, you can see the tech notes within the same ticket for the Incident ticket in the Problem ticket, and all of the Problem tech notes in the Incident ticket. Is this feature available for the Parent/Child relationship as well?
Unfortunately mate, this does not appear to be present maybe because the new Parent/Child relationship differs from Problem/Incident from a program code point of view. I guess a good feature to ask SolarWinds about. If they have almost the same code used in linking the I don't think it will take so much time to show all those notes in one view.