Tor: Can an exit relay read my traffic?

An exit relay can observe traffic between itself and an ordinary website when that traffic is not protected by HTTPS or another end-to-end encryption layer.

Short answer

An exit relay can observe traffic between itself and an ordinary website when that traffic is not protected by HTTPS or another end-to-end encryption layer. HTTPS protects the content in transit to the website. The exit still knows which destination it contacts, and a website still knows what you submit to it. Onion services do not use an exit relay for the final connection.

Sources

Tor Project: Secure connections, Tor Project: Onion services.