What is the shortcut to hide the navigator view in Apple Keynote?
Note that Navigatior View is designed to show the thumbnails for navigation.  Slide Only view shows only the slide without the thumbnails.
There is no built in shortcut to change views.  However, a custom keyboard shortcut can be added in the System Preferences.
To create a shortcut:

Go to System Preferences
Keyboard
Shortcuts Tab
Select App Shortcuts in the left pane
Click the Plus button
Set Application to Keynote from the dropdown
Type the Menu command EXACTLY as it appears in the menu
Choose a key combination

Now you can change view with custom shortcut.

Adding custom shortcut:


Switching views: