For Drupal 7, is there a hook debug mode equivalent to the theme debug mode?
You could create a custom module and use hook_module_implements_alter which takes two arguements - $implementations and $hook.

Try this:

function MODULE_module_implements_alter(&amp;$implements, $hook) {
  if ($hook == 'form_alter') {
    print_r($implementations);
  }
}


This will print out a list of all the implementations, in order, for hook_form_alter.