checkout_cart_add_product_complete

$this->_eventManager->dispatch(
            'checkout_cart_add_product_complete',
            ['product' => $product, 'request' => $this->getRequest(), 'response' => $this->getResponse()]
        );

$this->_eventManager->dispatch(
        'checkout_cart_product_add_after',
        ['quote_item' => $result, 'product' => $product]
    );

<?php
namespace StackExchangeMagentoAnswerObserver;

use MagentoFrameworkEventObserver;
use MagentoFrameworkEventObserverInterface;

class CheckoutCartProductAddAfter implements ObserverInterface
{

    /**
     * @param Observer $observer
     * @return void
     */
    public function execute(Observer $observer)
    {
        $quoteItem = $observer->getEvent()->getData('quote_item');
        $product = $observer->getEvent()->getData('product');
        $requestParams = $quoteItem->getBuyRequest();
        if ($requestParams instanceof MagentoFrameworkDataObject  && is_object($requestParams)) {
            // buyRequestArray is inddex
            $buyRequestArray = $requestParams->toArray();
        }
    }
}