Add source URL from Feed WordPress (Syndication) plugin to a custom field in post editor

by

What about the “syndication_permalink”? This is automatically pulled from the feed by FeedWordpress.

Then put something like 

<?php if (is_syndicated()) : ?>
     <p><a href="https://wordpress.stackexchange.com/questions/24222/<?php the_syndication_permalink(); ?>" target="_blank">Source</a></p>
  <?php endif; ?>

in your single post loop.