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 have multiple projects that use variations of the same base workflow. The variations depend on the requirements of the project or issue type. The variations mostly come in the form of new statuses ...
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