Shows the arguments of a newly registered post type right after it was registered. Helps inspecting which defaults have been added by core and if one of the developers arguments got overwritten. Simply add `&debug_pt_args=true` to your URL and set `WP_DEBUG` to `TRUE`.

debug_register_pt_args.class.php

<?php
defined( 'ABSPATH' ) OR exit;
/**
 * Plugin Name: (WCM) Debug Register Post Type Args
 * Description: Shows the arguments of a newly registered post type right after it was
 *              registered. Helps inspecting which defaults have been added by core and if
 *              one of the developers arguments got overwritten. Simply add
 *              <code>&debug_pt_args=true</code> to your URL and set
 *              <code>WP_DEBUG</code> to <code>TRUE</code> in your <code>wp-config.php</code>.
 * Plugin URl:  http://wordpress.stackexchange.com/questions/89066
 * Author:      Franz Josef Kaiser
 * Author URl:  http://unserkaiser.com
 * License:     MIT
 */

add_action( 'plugins_loaded', array( 'WCM_Debug_CPT_Args', 'init' ), 5 );
class WCM_Debug_CPT_Args
{
	protected static $instance;

	public static $builtin = array();

	public static $args = array();

	public static function init()
	{
		null === self::$instance AND self::$instance = new self;
		return self::$instance;
	}

	public function __construct()
	{
		if (
			! defined( 'WP_DEBUG' )
			OR ! WP_DEBUG
			OR ! isset( $_GET['debug_pt_args'] )
			OR true != $_GET['debug_pt_args']
		)
			return;

		add_action( 'registered_post_type', array( $this, 'get_args' ), 10, 2 );
		add_action( 'shutdown', array( $this, 'dump' ) );
	}

	public function get_args( $post_type, $args )
	{
		! $args->_builtin
			AND self::$args[ $post_type ] = $args;
	}

	public function dump()
	{
		if ( isset( self::$args ) )
			foreach ( self::$args as $pt => $args )
				printf(
					 '<h1>%s</h1><pre>%s</pre>'
					,$pt
					,var_export( $args, true )
				);
	}
}

Nice, is also in this helpful plugin: https://github.com/bueltge/Debug-Objects