How to add comment field in completed task notification (alert)

Summary:

When the owner gets the notification of completed task - he needs to see the comments added by performer

what is the field required to be added to the alert composer

Content (required):

Is there any method - to find the possible fields which can be added to the alert

Version (include the version you are using, if applicable):

22A

Code Snippet (add any code snippets that support your topic, if applicable):