Untitled

add_action('salesking_customers_custom_columns_header', function(){
    ?>
    <th class="nk-tb-col tb-col-md"><span class="sub-text"><?php esc_html_e('Last Order Date','salesking'); ?></span></th>
    <?php
});

add_action('salesking_customers_custom_columns_content', function($customer){
    $last_order = wc_get_customer_last_order($customer->get_id());
    $last_order_date = $last_order ? $last_order->get_date_created()->date('Y-m-d') : '-';
    ?>
    <td class="nk-tb-col tb-col-md" data-order="<?php echo esc_attr($last_order_date); ?>">
        <div>
            <span class="tb-amount"><?php echo esc_html($last_order_date); ?></span>
        </div>
    </td>
    <?php
}, 10, 1);