Non Object Notice Error – How to fix please

Replace your code with as mentioned below:

public function admin_body_class($classes) {

    global $wpdb, $post;

    $screen = get_current_screen();

    $status="parent-";
    if( isset( $post->post_parent ) && $post->post_parent > 0 ) {
        $status="child-";
    }

    $classes .= ' ' . $status . $screen->post_type;

    return $classes;

}