Toggling page views in Skim
I've just assigned custom shortcuts for the menu bar items.



You could also assign a shortcut to an AppleScript like this.

try
    tell application "Skim" to tell document 1
        if item -2 of (view settings as list) is single page then
            set view settings to {display mode:single page continuous}
        else
            set view settings to {display mode:single page}
        end if
    end tell
end try