Display Simple Product SKU, in WooCommerce loop pages, before item name

functions.php

<?php
/**
 * Display Simple Product SKU, in WooCommerce loop pages, before item name
 *
 * @return 	void
 */
function simple_product_sku_before_loop_item_title(){
	global $product;

	$type = $product->product_type;

	$sku = $type == 'simple' ? ' (#' . $product->get_sku() . ')' : '';

	echo $sku;
}
add_action('woocommerce_before_shop_loop_item_title', 'simple_product_sku_before_loop_item_title');

?>