Stubbs asks Johnny to go to the Red Light District in Port Tudor and get a photo of a fellow Congressan his and a hooker. Once you arrive at an alleyway near the district climb on the roof of the Port Tudor Weapons Depot. Once on the roof, Stubbs will call you and inform you that he is driving a red Cognoscenti. After a minute or so, the politician will arrive. Wait until the hooker starts talking to him and when that happens, quickly snap the photo. If done right, send it to Stubbs and drive away. After that just get off the roof and drive away and a little while later you will receive your payment and a call to Stubbs.