You can also listen to/view great works other players are offering to swap in the swap interface. I don't think there is a way to view someone else's great works otherwise (although coming to think about it, if you have a spy in someone else's city, I assume you could view the great works there the same way you can view anything else inside a city).
It's a bit strange that you cannot view the great works in the main culture victory interface (the one that lets you move works between different buildings and cities), though.