A little step forward... After reading this old doc

https://doc.odoo.com/6.0/developer/4_13_server_action/

I manage to replicate the function of the "reprint" button on POS Order.

Then I created an automated action to create (and print) the qweb report based on the order status "paid":

-Automated action-

Rule name: Kitchen_order

Related Document Model: Point of Sale

Active: yes

Sequence: 0

-Conditions-

When to Run: On Creation & Update

Filter: Paid

Actions:

Fields to Change

Set Responsible: Administrator

Add Followers: none

Server actions to run

Sequence: 1

Action Name: Reprint_Pos

Action To Do: Run a Client Action

-----------------------

Server Action:

Name: Reprint_Pos

Base Model: Point of Sale

Action To Do: Run a Client Action

Condition: True

Sequence: 1

Client Action: Receipt (Action Type is ir.actions.report.xml)

I've enable it on "More" tab and is working in both cases, I mean when I set it as a PDF or when I send it directly to my printer (using report to printer module).

Then I edit the "paid" function on Pos Workflow, adding my server action (Reprint_Pos) on Actions and leaving untouched all the other parameters.

Seems all good to me but the PDF is not generated automatically. Where I'm wrong?