I don’t know of any way to do this in Shotcut.
Would LOVE to see this added as a feature to Shotcut.
Shotcut is awesome, but most pro editing software that I’ve used have a button (or key command) to pull up the source frame up, in the source viewer, when you click the button or tap the key command. The functionality is called “Match Frame”, in the Avid.
This is hugely useful, as you say, when you mess up and you need to figure out where that 10 frame insert came from.
This software is so close to being feasible for a pro show.