In order to access the google remote desktop keyboard controls, you need to be on google chrome with the remote desktop plugin installed and enabled. At this point, start a session with the guest pc and you should see the blue arrow as described here:
On the right side of Chrome Remote Desktop, the small blue arrow has Keyboard controls and its submenu has the option to enable the clipboard.
The arrow can be seen here (its very small, but the red arrow is pointing to it.):
Clicking on it yields:
....where you can access remote desktop keyboard settings (key mappings, etc) as well as other features.