How can I see which orders have already been assigned to a route?

On your EasyRoutes for Shopify Orders page, access the Last route column, which will contain a link to the route any order was most recently added to:

If you're not seeing the Last route column on your Orders page, access your Configure table columns settings, found to the right of the map above your orders list:

From here, enable the Last route option from the Customer & Order Details section:

You can also use the Route filter to show only stops that have a route (or, alternatively, are not yet routed):

On EasyRoutes for Web, using the Route filter works the same way; however, the View Route button is nested within the Actions menu (three dots icon) for each imported order's entry: