“We conclude, as a matter of first impression, that a defendant may be convicted of human trafficking under G. L. c. 265, §50(a), so long as the jury find that the defendant knowingly trafficked another person, regardless of whether that person is specifically identified,” Justice Frank M. Gaziano wrote on behalf of the unanimous court. “Because the trafficking offenses at issue here were charged as ongoing criminal schemes, rather than as discrete instances of trafficking, we conclude that such an instruction was not warranted, and the trial judge did not err in declining to provide one.”