content-single-job_listing.php

$images = get_custom_field( 'job_multifile' );

if ( is_array( $images ) && ! empty( $images ) ){

	foreach( $images as $image ){
		$thumbnail_id = get_attachment_id_from_url( $image );
		$thumbnail = wp_get_attachment_thumb_url( $thumbnail_id );
		echo "<a href="{$image}"><img src="{$thumbnail}"></a>";
	}

} elseif( ! empty( $images ) ){

	$thumbnail_id = get_attachment_id_from_url( $images );
	$thumbnail = wp_get_attachment_thumb_url( $thumbnail_id );
	echo "<a href="{$images}"><img src="{$thumbnail}"></a>";
	
}