Since Cotonti 0.9.1 a new set of debugging facilities is available to template designers.
The first one is block/tags listing mode. It outputs a plain tree of blocks and assigned tags in them for the current page. Example:

To get such a debug page, you need to make sure debug_mode is enabled for your Cotonti instance first. Open datas/config.php and make sure you have debug_mode enabled:
$cfg['debug_mode'] = TRUE;
Then you can see a TPL dump of any page by simply appending tpl_debug=1...