Odoo-Build/snippets/account.report_invoice_document.get_position2.xml

<data inherit_id="account.report_invoice_document" priority="51">
    <xpath expr="//table[@name='invoice_line_table']//th[1]" position="before">
       
        <th id="position" class="text-start">
            <span>Pos.</span>
        </th>
    </xpath>
    <xpath expr="//table[@name='invoice_line_table']//t[1]/td[1]" position="before">
        
        <td id="position">
            <span t-esc="line.position"/>
        </td>
    </xpath>
</data>