From lostpedia.
Frank knows What Locke looks like :
Upon coming to a complete stop, a tree branch jutted through the window and killed the co-pilot instantly. After the crash, Frank attempted to gather all of the survivors together, yet Caesar took a leadership role, revealing to all the existence of buildings and cages on the island. Frank noticed Ben and Sun's departure from the camp, and decided to follow them.
Frank, Sun and Ben make their way to the outrigger canoes. ("Namaste")
Finding three outrigger canoes, Frank decided to join Sun and Ben on their trip to the main island. After Sun knocked Ben unconscious using an oar, Frank and Sun paddled the canoe from Hydra Island to the main Island, where they heard the sounds of the monster. They walked into the Processing Center, which seemed completely abandoned. Soon, a door creaked open, and Christian introduced himself to Frank and Sun. Christian took them to one of the houses, where he showed Sun a picture of DHARMA's new recruits in 1977. Sun was shocked to see Jack, Kate, and Hurley among them. Then, Christian informed her that she had a long journey ahead of her. ("Namaste")
A short time later, Ilana informed Locke that Frank took off with Sun in one of the three outriggers. ("The Life and Death of Jeremy Bentham")
Frank is knocked unconscious by a hostile Ilana. ("Dead Is Dead")
Christian told Frank and Sun to wait in the Barracks for John Locke, and to do what he says. When Ben went to investigate his old home he stumbled upon the two. They explained to him why they were there, but they did not believe Locke was alive, until Ben told them to look out the window. Locke came into the house and they talked about what to do next. Frank said he was returning to the Hydra Island to fix the jet radio and see if he could get help, with or without Sun. She decided to stay with Locke so she could find Jin, and Frank returned to the the Hydra Island in the outrigger. Upon his return, a flight 316 passenger named Jed told him that three of the survivors have found guns and claimed leadership of the group. When Frank confronted Ilana, she held him at gunpoint and asked: "What lies in the shadow of the statue?" Bewildered, Frank replied he had no idea what she was talking about, prompting her to knock him unconscious with the butt of her rifle. ("Dead Is Dead")