Roche is studying a handful of sites, including two in New Jersey, for a proposed clinical research center that could keep 240 jobs in the state after the drugmaker closes its campus in Nutley. The company, which originally expected to select a location by the end of August, said last week it is still in the process of deciding between the New Jersey sites and two others in New York. Darian Wilson, a Roche spokeswoman, would not identify the locations or discuss specific details, including a report published recently in NJBiz about company representatives visiting an office building in downtown New Brunswick, within close proximity to Robert Wood Johnson Medical School and Rutgers University.