How do I list available trade routes
You can view trade routes for cities which currently have an idle trader in them on the trade route overview (icon in the top right) and selecting the available trade route tab.
There is (currently) no way to view all available trade routes in all cities. (I agree this is a feature the developers should implement soon)
Since the release of the Rise and Fall expansion, it is now possible to review avaialble trade routes.
Just click the trade routes button (the circle of two arrows) in the top right menu:
