Is this Edit Post Screen?

Question

I believe you want something like this:

EDITED:

function function_name( $hook ) {
    global $post;

    if ( $hook == 'post-new.php' || $hook == 'post.php' ) {
        if ( 'post' === $post->post_type ) {
            // Do stuff
        }
    }
}

Script is hooked via:

add_action( 'admin_enqueue_scripts', array( $this, 'function_name' ) );

Is the metabox you are targeting created by a plugin? You will need to locate the appropriate hook or filter. There is likely an opportunity to filter the metabox markup before output.