Do you mean adding the priority column to the "Issues in Epic" panel that shows when you are viewing an Epic?
Sadly, this isn't possible in JIRA Cloud. These are similar questions where it is mentioned that it can't be done in JIRA Cloud:
There are a couple of suggestions raised in Atlassian's public issue tracker for this, which you might want to watch/vote on:
I hope this helps a little.
I’m a designer on the Jira team. For a long time, I’ve fielded questions from other designers about how they should be using Jira Software with their design team. I’ve also heard feedback from other ...
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