Can’t get page content in WordPress

Wrap the_content() function like below

$args = array(
  'post_type' => 'your-custom-post-type',
);
$query = new WP_Query( $args );
while( $query->have_posts() ):
   $query->the_post();
   the_content();
endwhile; wp_reset_postdata();

one thing to note here though, you must know where to end the loop ( i.e., endwhile; )
as you’ve other markup in the page template ( I assumed that above code belongs to post-template.php )

Another thing I noticed, if the post-template.php is template for about us page, then you can get content by

selecting respective page template for about us page in wordpress backend.

then,

while( have_posts() ):
  the_post();
  the_content();
endwhile; wp_reset_postdata();