Fn+Ctrl+F8 will highligh the Finder menu bar icons on the right, arrows will navigate you to the Keyboard preferences icon.
Depending on how you have your Function keys configured, the Fn is optional. Of note, Fn+Ctrl+F2 will activate the Finder menu bar's Apple icon on the left hand side.
In macOS Sierra you can also use Siri to help with this. Invoke Siri with whichever keyboard shortcut you choose from System Preferences >> Siri::Keyboard Shortcut, for example Option+Spacebar
...then say "Turn on the Keyboard Viewer"
...and voila:
Unfortunately, Siri will not close the Keyboard Viewer, nor will command w