How to associate specific activities with specific events/metrics we create?

Hi. 

We use Klavyio to send transactional emails to our customers who send inquiries/book vendors on our marketplace. Using Klavyio API we can get information about all emails (metrics) that we have sent to the customer. However, we cannot associate specific emails with specific inquiries/bookings. We want to understand if the customer has opened specific email and when he did that. Does anybody now to connect specific activities (email delivered, email opened) with a specific event? 

Thank you in advance!