How do I examine the symfony event handlers that are active?
This maybe not best practice but something like this will list all the events and their handlers:

 $kernel = \Civi::service('civi_api_kernel');                                
 $this-&gt;dispatcher = $kernel-&gt;getDispatcher();                             
 $listeners = $this-&gt;dispatcher-&gt;getListeners();                             
 foreach ($listeners as $event =&gt; $event_listeners) {                        
   echo "\n\n# $event\n";                                                    
   foreach ($event_listeners as $n =&gt; $listener) {                           
     echo "\n## Listener $n";
     $reflection = new \ReflectionClass($listener[0]);                       
     echo $reflection-&gt;getName() . "::" . ($listener[1]);
     echo "\nsource: " . $reflection-&gt;getFileName()                          
       . " lines: " . $reflection-&gt;getStartLine()
       . "-" . $reflection-&gt;getEndLine();
     // echo "\n Methods:" . json_encode(get_class_methods($listener[0]),JSON_PRETTY_PRINT);
   }   
 }