I have added the product into the cart and want to send email to the customer after the same product's price change from the backend.
You need to elaborate your question to get proper answer. Like - What kind of Operation do you want to perform and when you need to perform after product price updated from the backend?
One such example - If you want to update the product price of the item added to the cart then you should use Object Manager:
$cart = $objectManager->get('\Magento\Checkout\Model\Cart'); $priceHelper = $objectManager > create('Magento\Framework\Pricing\Helper\Data'); $items = $cart->getQuote()->getAllItems();