Add Product Permalink in woocommerce admin order page

There’s no permalink property of a product. Permalinks are not stored in the database, because they’re generated based on a number of external factors. Therefore you need to use a function to retrieve the permalink. In WooCommerce the best way to do this is with:

function fpd_custom_order_item_values($_product) {
    $url = $_product->get_permalink();

    echo '<p>' . esc_url( $url ) . '</p>';
add_action( 'woocommerce_before_order_itemmeta', 'fpd_custom_order_item_values', 100, 1);

Also, make sure you’re escaping your output. Since this is a URL, use esc_url().