By default, a task requester/ assigner does not receive email notifications for the changes on the tasks that they assign to other users. The amount of notifications on these tasks would be overwhelming for someone who assigns a large number of tasks routinely.
The New Task button does not show in the subtask section when there is an Approval on the main task.
The New Task button does not show because Adobe Workfront does not allow a task with an Approval to become a parent task.
The Allocation Date is the first day (Sunday) of a week in which the allocation of a Job Role to a task starts. For information, see Glossary of Adobe Workfront terminology.