newsupernova/vendor/magento/module-offline-payments/view/adminhtml/templates/info/purchaseorder.phtml

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
/**
 * @var $block \Magento\OfflinePayments\Block\Info\Purchaseorder
 */
?>
<div class="order-payment-method-name"><?= $block->escapeHtml($block->getMethod()->getTitle()) ?></div>
<table class="data-table admin__table-secondary">
    <tr>
        <th><?= $block->escapeHtml(__('Purchase Order Number')) ?>:</th>
        <td><?= $block->escapeHtml($block->getInfo()->getPoNumber()) ?></td>
    </tr>
</table>