I asked a friend for help and solved it like this
<?php $thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'NAME_OF_THE_THUMBNAIL_KIND' ); $url = $thumb['0']; ?>
<div id="featured" data-parallax="scroll" data-speed="0.1" data-natural-width="2304" data-natural-height="1536" data-ios-fix="true" data-position="top" data-bleed="10" data-image-src="https://wordpress.stackexchange.com/questions/220324/<?php echo $url ?>">