If you access the subtask you'll be able to see the parent in the top of the screen, even on the search screen.
If you want to search for subtasks of a specific parent, you can use the function (subtasksOf).
I hope it was helpful.
Jaime Kirch da Silveira
Atlassian Cloud Support
I am also looking for this, it is works sorting by key but only if you add them in order - but not being perfect I find I missed one and have to enter it later. there is no way to see the task and it relatives at a high level list on the issue screen, there are many sort options there but you have to know the name of the sort field to access it. I checked them out using one letter at a time. This is a biggie for me going forward.
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