hasn't_thumbnail_post_list.php

<?php 

// Query args.
$args = array(
	'post_type' => 'post',
	'posts_per_page' => -1,
);

$query = new WP_Query( $args );

// Start the loop.
while ( $query->have_posts() ) : $query->the_post();

	if ( !has_post_thumbnail() ) { // check if the post hasn't a Post Thumbnail assigned to it
		echo get_the_title().'<br/>';
	} 			

// End the loop.
endwhile;

// Restore original Post Data 
wp_reset_postdata();

?>