Add product SKU underneath the product title on an order form from Order Form for WooCommerce. Requires version 1.0.5 or higher. Save this file as a simple plugin in the WordPress plugins folder. http://orderform-woo.webaware.net.au/

order-form-woo-sku.php

<?php
/*
Plugin Name: Order Form for WooCommerce SKU
Plugin URI: https://gist.github.com/webaware/7a8974a88caf4bcb3eed
Description: add product SKU to Order Form for WooCommerce product
Author: WebAware
Author URI: http://webaware.com.au/
*/

if (!defined('ABSPATH')) {
    exit;
}

/**
* add product SKU to Order Form for WooCommerce product
* @param WC_Product $product
* @param array $attrs
*/
add_action('orderform_woocommerce_order_item_end', function($product, $attrs) {

    $sku = $product->get_sku();

    if (wc_product_sku_enabled() && ($sku || $product->is_type('variable'))):

        if (empty($sku)) {
            $sku = __('N/A', 'woocommerce');
        }
        ?>

            <br />
            <span class="sku_wrapper"><?php _e( 'SKU:', 'woocommerce' ); ?> <span class="sku" itemprop="sku"><?php echo $sku; ?></span>.</span>

        <?php
    endif;

}, 10, 2);