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.
If you spend enough time as a Jira admin - whether you are managing a single, mid-sized instance, a large enterprise one or juggling multiple instances at once - you will eventually find yourself in ...
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