Who attacks Zaman?

Farid attacks Zaman, the director of the orphanage, for selling children to the Taliban. Zaman thinks he's doing the kids a favor, as there is a chronic lack of food, medicine, and blankets at the orphanage. Things are so bad there that one child froze to death during the winter. Selling orphans to the Taliban may be morally dubious, to say the least, but Zaman figures that if it will save their lives, and there's no alternative, then so be it. And, in any case, Zaman is not really in a position to defy the Taliban; they are, after all, a deadly terrorist organization that would think nothing of killing Zaman, or anyone else who got in their way. Nevertheless, this whole episode illustrates the moral, as well as economic, decline of Afghanistan since Amir and Baba left for America.

Short Answer: Farid attacks Zaman in the orphanage's office.
In chapter 20, Amir and Farid visit a local orphanage in hopes of finding and saving Sohrab. When they arrive at the orphanage, Zaman answers the door and introduces himself as the director. In his office, Zaman laments about the lack of money and resources needed to run such a crowded orphanage. Zaman then carefully tries to explain to Amir how he can go about getting Sohrab and tells him that there is a Taliban official who regularly visits the orphanage with money. Farid immediately criticizes Zaman for selling the children instead of protecting them and begins to menacingly walk toward him. When Zaman begins to make excuses, Farid attacks him and leaps over the table. Farid proceeds to strangle Zaman, and Amir intervenes by pulling Farid off of the director. Farid loosens his grip once Amir yells that the children are watching and spits in Zaman's face before he walks out of the office.