This might get you started, but without knowing your end game, I have no idea what to aim for:
SELECT X.N.value('@label','nvarchar(50)') AS [Type],
       C.T.value('@label','nvarchar(50)') AS Label,
       C.T.value('@id','nvarchar(50)') AS id
FROM @XML.nodes('/navigation/content') X(N)
    CROSS APPLY X.N.nodes('./content') C(T);


Edit: Des was way ahead of me while I had to (once again) Google how to use XQuery 😛