...
- Click on "Issue Fields" tab.
- Select the "Assignee" field from the from
Select a field;
the help shows you how to access the field, its sub-fields and test the field value. - Click on one of the expressions to insert it into the editor; the help shows you the supported properties and methods of the returned Data Type.
Another way is to go to the "Data Types" tab of the Jira expressions editor and select "Issue" from "Select a Data Type" field. The help lists properties and methods of the Issue data type. Click on a button to insert it into the editor; hover over it to get the information.
Structure of the transition
variable
...