Enqueue script on specific WooCommerce template

I would like to enqueue a lightbox script on the WooCommerce page content-single-product.php.

I have tried the following via functions.php:

if(is_page_template( 'page-gallery.php' ) || is_page_template( 'content-single-product.php' )) {
        wp_enqueue_script( 'theme-lightbox', get_template_directory_uri() . '/js/lightbox.js', array(), '20150323', true );
}

The script loads correctly on page-gallery.php, but not on the WooCommerce single product page. I assume this method only works for my theme page templates?

You need to delay the firing of your code, otherwise your conditionals will evaluate false (the request won’t have been parsed yet). Use the action wp_enqueue_scripts:

function wpse_182357_enqueue_scripts() {
    // Your code
}

add_action( 'wp_enqueue_scripts', 'wpse_182357_enqueue_scripts' );

Update: Missed the root of the problem – is_page_template() only works for pages. Rather than checking if the current template file is content-single-product.php, check if the request is for a single product with is_singular():

is_singular( 'product' );