Composer John Adams’ and librettist Peter Sellars’ opera, “El Niño,” debuted at Metropolitan Opera earlier this year, making this their fourth work to be produced at the Met, including “Doctor Atomic” (2008), “Nixon in China” (2011), and “The Death of Klinghoffer” (2014). OperaWire reviewed the production in addition to attending and documenting Guggenheim Museum’s “Works & Process” presentation by the {…}