Classic Workflow Tasks in the Change Order object support a field for comments in the task details screen. But Incident, Problems and Requests with Classic workflows do not have the same Comments field on the task details. Why is it ?
Work around is to create a custom comments column on cr_wf object and expose it on detail_cr_wf.htmpl, similar to adding a custom column on any other Service Desk Manager form/object.
For more information on how to use Web Screen Painter see this link: https://docops.ca.com/ca-service-management/17-1/en/building/building-ca-service-desk-manager/web-interface-modifications/how-to-modify-schema-using-web-screen-painter