Below Code will generate Select box of post type “resources” change this value as per your post type.
<select name="page_id" id="page_id" class="archive-dropdown" onchange="document.location.href=this.options[this.selectedIndex].value;">
<option value="">Select Resource Post</option>
<?php
global $post;
$args = array( 'numberposts' => -1,'post_type'=>'resources');
$posts = get_posts($args);
foreach( $posts as $post ) : setup_postdata($post); ?>
<option value="<? echo get_permalink($post->ID); ?>"><?php the_title(); ?></option>
<?php endforeach; ?>
</select>
It works for me.
thanks