Odoo-Build/snippets/mint_system.purchase.report_purchaseorder_document.show_default_code.xml

<data priority="50">

  <xpath expr="//table/thead/tr/th[1]" position="after">
    <th>
      <span>Artikel Nr.</span>
    </th>
  </xpath>
  <xpath expr="//table/tbody/t/tr/t[1]/td[1]" position="after">
    <td>
      <span t-field="line.product_id.default_code"/>
    </td>
  </xpath>
  
</data>