The Delivery due date notification workflow is closely related to purchase requisitions and confirmation of receipt. Usually, the information in a purchase order comes directly from a purchase requisition. However, you can select a requester in the purchase order itself. The requester is the person who receives notifications about the purchase order.
First, you must relate a user to a person who can be used as the requester:
  

A Confirmation of product receipt policy needs to be set up: 

(Procurement and sourcing -> Setup -> Policies -> Confirmation of product receipt policies)


In this example, a policy has been created for vendor 3105, but you can  create a policy for any vendor or all vendors
A Delivery due date notification workflow needs to be set up: 

(Procurement and sourcing -> Setup -> Procurement and sourcing workflows)

 
Work item subject and Work item instructions needs to be specified:
The Assignment is set to Participant:
 

Type of participant is set to Product receipt participant, and Participant is set to Requisitioner from the purchase order line:
 
A Batch job for delivery due date notification workflow needs to be set up: 

(Procurement and sourcing -> Periodic -> Purchase orders -> Batch job for delivery due date notification workflow) 


In this example, the notification will be shown on the day of delivery
In case a batch server is not available, you must start the Tutorial_WorkflowProcessor: 

(AOT -> Forms -> Tutorial_WorkflowProcessor)

  
A Requester must be set on the purchase order.: 


Notice that the vendor matches the vendor from the Confirmation of product receipt policy and that I have selected a requester.
The requester can now be seen on all of the purchase order lines:
After you confirm the purchase order, a notification will appear when it is picked up by the batch job:

 Now the requester can go to Enterprise Portal and receive the product: 


Note: The first machine did not have Enterprise Portal installed, so I switched to another machine. Therefore, the purchase order ID is different in this screenshot.

https://technet.microsoft.com/en-us/library/hh545540.aspx