Unable to display custom fields on WooCommerce product pages

Where are you pasting that code?

The code snippet needs to be put in the right spot.
So you need to copy the content-product.php template from the woocommerce plugin folder and place it in your theme folder in a “woocommerce” folder.
Then paste that code within the Loop.

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Updated Answer:

Okay so I believe that you need to use the get_post_custom function.

Take note of the Name of your custom field. Then we can something like this to output the results:

<?php

  $custom_fields = get_post_custom($post->ID);
  $my_custom_field = $custom_fields["Name of your Field"];
  foreach ( $my_custom_field as $key => $value ) {
      echo "<strong>$key: </strong> $value <br />";
  }

?>