Get SKU from products in an order

gistfile1.php

<?php

$order = new WC_Order( $order_id );

foreach ( $order->get_items() as $item_key => $item ) {

	$product = $order->get_product_from_item( $item );
	
	$sku = $product->get_sku();
	
	// print_r( $item );
}