Holland & Knight LLP partner Mark A. Flessner will succeed Edward N. Siskel as the city of Chicago’s top attorney, Mayor-elect Lori Lightfoot announced Wednesday.Flessner is a 12-year veteran of the U.S. Attorney’s Office in Chicago, the same office Lightfoot worked in.As part of Flessner’s current practice he helps clients deal with inquiries by government agencies. Flessner was one of the lawyers who …