the_post_thumbnail() displays the featured image. get_the_post_thumbnail() retrieves it for use in code. Try something like this:
<?php
$featured_image = get_the_post_thumbnail( get_the_ID() );
$fi_src = $featured_image['src'];
$slider = get_the_post_thumbnail( get_the_ID(), 'sliderimage' );
$s_src = $slider['src'];
?>
<img src="https://wordpress.stackexchange.com/questions/130312/<?php echo $fi_src; ?>" data-thumb=""<?php echo $s_src; ?> title="" />