Users who have the permission level of Administrator, have the ability to make a client configurable change which allows for the flag of Notify Owner to be set to Y as default, on creation of Runbooks.  This means that for every Runbook which is created in the client instance, Notify Owner will be enabled for all tasks. To enable this feature you can do so via the Admin option on the left hand menu and select Configuration.

By enabling the Notify Owner Default, each time a Runbook is created by default Notify Owner will be enabled on all Tasks.

Although Notify Owner may have been selected to Default to Y on creation of the Runbook this feature can be taken off either when creating the Runbook, or by updating the Runbook via the Details screen.

If by default you do not have Notify Owner enabled, you can still add this on a Runbook by Runbook basis during the creation process by enabling the checkbox, or from the Runbook Details screen.

Notify owner can also be added on a Task by Task basis in the same way, from the Task Details screen.