The key, I think, to what you are doing is to use “offset”
<div class="col4 inner-left">
<ul class="popular-list">
<?php
query_posts('order=DESC&posts_per_page=3&post_type=pop');
if (have_posts()) : while (have_posts()) : the_post(); ?>
<li>
<a href="https://wordpress.stackexchange.com/questions/125200/<?php the_permalink(); ?>"><?php the_title(); ?></a>
</li>
<?php endwhile; endif; ?>
</ul>
</div>
<div class="col4 inner-right">
<ul class="popular-list">
<?php
query_posts('order=DESC&posts_per_page=3&post_type=pop&offset=3');
if (have_posts()) : while (have_posts()) : the_post(); ?>
<li>
<a href="https://wordpress.stackexchange.com/questions/125200/<?php the_permalink(); ?>"><?php the_title(); ?></a>
</li>
<?php endwhile; endif; ?>
</ul>
</div>
<?php // Reset Query
wp_reset_query(); ?>
http://codex.wordpress.org/Class_Reference/WP_Query#Pagination_Parameters