(This is part two of a two-part series. Part one was published on Monday.)The second issue in a case where Walworth Investments, a company owned by a prominent Chicago family, claims it lost hundreds of millions of dollars — after it was allegedly duped into selling its 21% interest in Mu Sigma Inc. for $9.3 million a few years before the startup’s value soared to $1.5 billion — was whether Mu Sigma’s chairman-chief executive, Dhiraj C. Rajaram, violated a fiduciary duty of full disclosure when he …