exiting fullscreen mode of Hyper V client
Whenever I nest RDP sessions or RDP -> VM sessions I always unstick the initial RDP sessions toolbar (clicking the tack icon will toggle it). This will cause it to slide out of view revealing the secondary connection bar of the nested RDP or VM window session. Now if you go three levels deep, you're on your own :).
Ctrl+Alt+Pause should get you out of full-screen mode when using hyperV in full screen mode inside a remote desktop session.
None of the suggested key combinations bring me out of hyperv fullscreen mode. However, I found a two key sequence workaround. Pressing ctrl+alt+left-arrow causes the notebook to rotate display -90 degrees and releasing fullscreen mode. Quickly follow with ctrl+alt+up-arrow to restore normal mode. You are now out of fullscreen mode.