To create job custom field in Workday, follow these steps
Search for 'Create Custom Object'
Create Custom Object
Click 'Field Definitions'
Click 'Add' button
Enter Label & Field Type
Select 'Job Requisition Data'
Review and Confirm
Configure Field Selection
Activate Custom Object
Search for 'Business Process Definitions'
Click 'OK'
Find and Edit Business Process Definition
Click 'Edit Definition'
Click 'OK'
Configure Business Process Steps
Verify and Complete