NSArray *anArray = @[ @{@"identifier1": @{ @"3498239502323120": @{@"key1":@"abc",
                                                                      @"key2": @123},
                                               @"3493208429034821": @{ @"key1": @"def",
                                                                       @"key2": @456}

                                            },
                            @"identifier2": @{ @"456434234234": @{ @"key1": @"ghi",
                                                                   @"key2": @789 },
                                               @"8796554": @{ @"key1": @"jkl",
                                                              @"key2": @101112 }
                                                }
                            }];

    NSArray *identifier1 = [anArray valueForKeyPath:@"identifier1"];
    NSLog(@"identifier1: %@", identifier1);
    NSMutableArray *values = [[NSMutableArray alloc] init];
    for (NSDictionary *aDict in identifier1)
    {
        NSArray *subdictionaries = [aDict allValues];
        [values addObjectsFromArray:[subdictionaries valueForKey:@"key1"]];
        for (NSDictionary *aSubdict in subdictionaries) {
//                  OR
//            NSString *aValue = aSubdict[@"key1"];
//            if (aValue)
//            {
//                [values addObject:aValue];
//            }
        }
    }

    NSLog(@"Values: %@", values);