Dear.
Actually the tool (12.6.4) does not have notifications approvals or rejections for task-level workflow.
WHAT can be done by analyzing the process is:
1) In order to set the notification for approval a Policy xpress executed when the task is completed. For when the task is completed, it has been approved.
2) In order to set the notification for denial of a Policy Xpress executed when the event occurs "ModifyUserEvent" in their status "Declined".
Obs .: These are outline measures being highly recommended to be implemented in the possibility that we can configure these notifications exactly when a task is rejected or approved tool.