There is none for that rule specifically - I have put in a support ticket for this as it does not feel like intentional behavior.
Workfront has "All Predecessor Task Completion to Task Dependents" which will send a notification, but only if the predecessor is on the task the user is assigned to. This does not work for sub tasks with a predecessor on the parent task. I tested with a report, sub tasks with predecessor parents switch the field canStart from false to true, but this does not trigger an event notification.
The fix from Workfront would be to change the trigger for "All Predecessor Task Completion to Task Dependents" to watch the canStart field.