Assuming you’ve followed the instructions to install JSON-Framework into your project, here’s how you use it (taken from the docs here) :
// Parse the string into JSON
NSDictionary *json = [myString JSONValue];
// Get the objects you want, e.g. output the second item's client id
NSArray *items = [json valueForKeyPath:@"data.array"];
NSLog(@" client Id : %@", [[items objectAtIndex:1] objectForKey:@"clientId"]);