That request looks right as long at you’re replacing “alias” with and actual alias and “CIK” with the actual CIK of the client that owns that aliased data port.
coap://coap.exosite.com/1a/temp?6d18765178325a8b4ba2b4e35786ff5ba599f150 works for me in Copper.
I’m not sure why you’d be getting a 401, just make sure that you’ve copied the CIK correctly and if you’re using a device type other than “generic”, make sure that it has been activated (In the device information popup in portals you should see “Status: Activated”).
IPv6 works exactly the same way. If your computer has an IPv6 connection you may even already be using IPv6 when sending requests from Copper. If you want to force IPv6, you can use the domain coap6.exosite.com, but you should really only use that domain for testing.