How to get the WordPress post thumbnail (featured image) URL?

Simply inside the loop write `<?php the_post_thumbnail_url(); ?>` as shown below:-

$args=array('post_type' => 'your_custom_post_type_slug','order' => 'DESC','posts_per_page'=> -1) ;
$the_qyery= new WP_Query($args);

if ($the_qyery->have_posts()) :
while ( $the_qyery->have_posts() ) : $the_qyery->the_post();?>

<div class="col col_4_of_12">
<div class="article_standard_view">
<article class="item">
<div class="item_header">
<a href="<?php the_permalink(); ?>"><img src="<?php the_post_thumbnail_url(); ?>" alt="Post"></a>
</div>

</article>
</div>
</div>
<?php endwhile; endif; ?>