original website post link after post

In your theme you can add code like this in to the template for your single posts (might be single.php or content-single.php or similar)

<?php if (is_syndicated()) : ?>
	<!-- if is FeedWordpress post -->
		<p>This is a syndicated post. You can view the original post here: <a href="<?php the_syndication_permalink(); ?>"><?php the_title(); ?></a>.</p>
	<?php endif; ?>