This looks like how you should use WCK:
<?php
foreach( get_cfc_meta( 'testimonialsbox' ) as $key => $value ){ ?>
<?php $author_testimonial = $key['author_testimonial']; ?>
<?php $photo_obj = get_cfc_field( 'testimonialsbox','photo', false, $key ); ?>
<div class="col-md-6 col-sm-6">
<?php echo $author_testimonial; ?>
<div class="author-det">
<img src="https://wordpress.stackexchange.com/questions/279399/<?php echo $photo_obj["url'] ?>" alt="https://wordpress.stackexchange.com/questions/279399/<?php echo $photo_obj["alt']; ?>"/>
</div>
</div>
<?php } ?>