Odoo-Build/snippets/purchase.report_purchaseorder_document.add_discount.xml

<data inherit_id="purchase.report_purchaseorder_document" priority="50">
    <xpath expr="//th[@name='th_price_unit']" position="after">
        <th name="th_discount" class="text-end">
            <strong>Discount</strong>
        </th>
    </xpath>
    <xpath expr="//td/span[@t-field='line.price_unit']/.." position="after">
        <td id="td_discount" class="text-end">
            <span t-out="line.discount" t-options="{&quot;widget&quot;: &quot;integer&quot;}"/><span> %</span>
        </td>
    </xpath>
</data>