The phrase "assembled reporters" refers to a group of journalists or news media professionals who have gathered together for a particular event or purpose. Full definition
The star mingled incognito for a few minutes in the press area of a giant sports hall in the Midlands city - to the bemusement of assembled reporters. (mirror.co.uk)
After a marathon Friday press conference at which de Blasio answered dozens of questions from assembled reporters on a wide variety of subjects, the mayor had a quiet weekend. (gothamgazette.com)
He also mentioned that he would consider a halt to all offshore drilling, and told assembled reporters that the Department of the Interior had expanded the former buffer zone in the Channel by an additional 34,000 acres (140 km2), and was converting the previous buffer zone into a permanent ecological preserve. (en.wikipedia.org)