1) make sure you have an instance running
2) select it in the "Cloud view"
3) open "Properties (view)" for it
4) select the Hostname row and choose "Copy" in the context menu
5) paste it somewhere (ex. console, text editor)
Result:
You get the Hostname preceeded by "Hostname"
ex. if you have an instance which has the hostname ec2-75-101-219-33.compute-1.amazonaws.com you'll get "Hostname ec2-75-101-219-33.compute-1.amazonaws.com" in your clipboard