Add product SKU column before item (title) column on an order form from Order Form for WooCommerce. Requires version 1.4.0 or higher. Save this file as a simple plugin in the WordPress plugins folder. http://orderform-woo.webaware.net.au/

order-form-woo-sku-column.php

<?php
/*
Plugin Name: Order Form for WooCommerce SKU
Plugin URI: https://gist.github.com/webaware/a75e83ede1607536642b
Description: add product SKU column to Order Form for WooCommerce product
Author: WebAware
Author URI: http://webaware.com.au/
*/

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

/**
* add column head for SKU
* @param array $attrs
*/
add_action('orderform_woocommerce_before_order_item_head', function($attrs) {
    ?>
    <th class="orderform-woocommerce-order-sku">SKU</th>
    <?php
});

/**
* add column foot for SKU
* @param array $attrs
*/
add_action('orderform_woocommerce_before_order_item_foot', function($attrs) {
    ?>
    <td class="orderform-woocommerce-order-sku">&nbsp;</td>
    <?php
});

/**
* add column for SKU
* @param array $attrs
*/
add_action('orderform_woocommerce_before_order_item', function($product, $attrs) {
    $sku = wc_product_sku_enabled() ? $product->get_sku() : '';
    ?>

        <td class="orderform-woocommerce-order-sku">
        <span class="sku" itemprop="sku"><?php echo $sku; ?></span>
        </td>

    <?php
}, 10, 2);