get all Observer in Magento2 for specific event

the easy way is to go to this file 

\vendor\magento\framework\Event\Manager.php

then go to this function dispatch

you can now user this 

foreach ($this->_eventConfig->getObservers($eventName) as $observerConfig) {
    if ($eventName == "catalog_product_save_after") {
         $all_observers = print_r($observerConfig, true);
    }
}