catch order place after event magento2

You can try with below code in your observer and check,

class Orderneo implements \Magento\Framework\Event\ObserverInterface
{
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
     $order = $observer->getEvent()->getOrder();
     echo $orderId = $order->getId();
     $comment = $this->getRequest()->getParam('comment');
     print_r("Catched event succssfully !"); exit;
    }
}

better use this event instead of sales_order_save_after and checkout_onepage_controller_success_action

checkout_submit_all_after.

it will work even site not redirected to success page because of some errors like internet issue and all.

You can use checkout_onepage_controller_success_action and sales_order_save_after event while after order placing event.

But you can not use print_r(),die(); and exit(); for debugging. So you can use log method for debugging here.

you can use print_r(),die();,exit(); and also log method in checkout_onepage_controller_success_action event.

while useing checkout_onepage_controller_success_action event

Filepath:app\code\Vendorname\Modulename\etc\frontend\events.xml

<event name="checkout_onepage_controller_success_action">
    <observer name="mymodule_controller_success_action" instance="Vendorname\Modulename\Observer\MyObserver"  />
</event> 

Filepath:app\code\Vendorname\Modulename\MyObserver.php

<?php
namespace Vendorname\Modulename\Observer;

use Magento\Framework\Event\ObserverInterface;

class MyObserver implements ObserverInterface
{
      public function execute(\Magento\Framework\Event\Observer $observer)
    {
     $order = $observer->getEvent()->getOrder();
     echo $orderId = $order->getId();
     print_r("Catched event succssfully !"); 
     exit;
    }

}

while using sales_order_save_after event

Filepath:app\code\MyCompany\MyModule\etc\frontend\events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="sales_order_save_after">
        <observer name="mymodule_sales_order_save_after" instance="MyCompany\MyModule\Observer\MyObserver" />
    </event>
</config>

Filepath:app\code\MyCompany\MyModule\MyObserver.php

  <?php namespace MyCompany\MyModule\Observer; 
    use Magento\Framework\Event\ObserverInterface; 

    class MyObserver implements ObserverInterface { 


        public function execute(\Magento\Framework\Event\Observer $observer) { 
            $order = $observer->getEvent()->getOrder();
            $customerId = $order->getCustomerId();
            $writer = new \Zend\Log\Writer\Stream(BP . '/var/log/templog.log');
            $logger = new \Zend\Log\Logger();
            $logger->addWriter($writer);
            $logger->info('Catched event succssfully');

       }
   }