Post type no single page

First, before you start, just reflush your permalinks. It is sometimes strange why the Template Hierarchy fails. You code checks out, and should in theory work. Everything checks out, and to make sure, I tested it on my side.

You can use this work around to “force” wordpress to use a template. Here we would use template_include filter hook.

<?php
function wpse_template_include( $original_template ) {
    if ( isset( $wp->query_vars['job'] ) && false == $wp->query_vars['job']  ) {
        return get_template_directory() . '/single-job.php';
    } else {
        return $original_template;
    }
}

add_filter( 'template_include', 'wpse_template_include' );