You can post on friends wall by using FBWebDialogs class of Facebook SDK. For that you need friends facebook id in parameters in dictionary as below
    NSMutableDictionary *parmaDic = [NSMutableDictionary dictionaryWithCapacity:5];
    [parmaDic setObject:link forKey:@"link"];            // if you want send picture
    [parmaDic setObject:@"NAME" forKey:@"name"];         // if you want to display name
    [parmaDic setObject:message forKey:@"description"];  // if you want to display  description
    [parmaDic setObject:@"FRIEND_FACEBOOK_ID" forKey:@"to"];
    [parmaDic setObject:@"LOGO_URL" forKey:@"picture"];  // if you want to send App logo
    [FBWebDialogs presentFeedDialogModallyWithSession:nil parameters:parmaDic handler:^(FBWebDialogResult result, NSURL *resultURL, NSError *error)  {
        if (error) {
           // Case A: Error launching the dialog or sending request.
           // NSLog(@"Error sending request.");
        } else {
                if (result == FBWebDialogResultDialogNotCompleted) {
                    // Case B: User clicked the "x" icon
                    //    NSLog(@"User canceled request.");
                } else {    
                        //   NSLog(@"Successfully Invited.");
                  }
               }
         }];
4
solved How to post text on friends wall using latest facebook sdk in IOS