How to show testcase custom field in coverage section of jira issue

If I understand correctly, you would like to see a Zephyr Scale custom field displayed in a Jira Issue by clicking on the Zephyr Scale button.  I haven't seen a way to do this yet.  You could add a field into the Create issue form to include the custom data you want to display but it would be separate to the Zephyr Scale test case custom field and not linked.