Sean "Diddy" Combs hired a lawyer as a federal grand jury in Manhattan continues a months-long investigation into sex-trafficking allegations. Jordan Strauss/AP Images; BIA Manhattan federal grand jury is weighing sex-trafficking allegations against Sean 'Diddy' Combs.The rap mogul hired top NYC defense lawyer Marc Agnifilo to fight a possible indictment.Agnifilo has repped Harvey Weinstein, 'pharma bro' Martin Shkreli, and NXIVM leader Keith Ra…