Probably less common today but honestly I'd be surprised if someone didn't know it at all. Try asking someone over fifty in England what "use your nous" means.
A quick dip into Google Books throws back this from the works of George Garrett, a Liverpool-born working class writer who wrote about being a merchant seaman during World War I: "An older fireman stopped them. 'Use your nous,' he sang out. 'You can't pile into another room and waken all hands for the sake of an individual."
Or this from The Spectator in the 80s: "Use your nous, you silly cow"
