Magento – how to get all coupon code which can apply on cart page in magento 2

You can do one thing when any user enter the coupon code for particular product and press apply button you can put ajax link url will be

http://localhost/magento/index.php/checkout/cart/updatePost/

and create one observer checkout_cart_update_items_before write your code for apply coupon.

If you've already generated the codes and associated them with a rule, you can look the code up by the rule id. We recently did something similar but had the codes auto generated based on rule id - I found this extension helpful:

http://www.magentocommerce.com/magento-connect/newsletter-subscription-with-free-gift-coupon.html

It may not be exactly what you're looking for, but you could modify it to suit your needs.