woocommerce_order_item_name.php

<?php
/**
 * Add custom cart item data to emails
 */
function plugin_republic_order_item_name( $product_name, $item ) {
  if( isset( $item['pr_field'] ) ) {
    $product_name .= sprintf(
      '<ul><li>%s: %s</li></ul>',
      __( 'Your name', 'plugin_republic' ),
      esc_html( $item['pr_field'] )
     );
  }
  return $product_name;
}

add_filter( 'woocommerce_order_item_name', 'plugin_republic_order_item_name', 10, 2 );