tap gesture recognizer - which object was tapped?

Define your target selector(highlightLetter:) with argument as

UITapGestureRecognizer *letterTapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(highlightLetter:)];

Then you can get view by

- (void)highlightLetter:(UITapGestureRecognizer*)sender {
     UIView *view = sender.view; 
     NSLog(@"%d", view.tag);//By tag, you can find out where you had tapped. 
}

Its been a year asking this question but still for someone.

While declaring the UITapGestureRecognizer on a particular view assign the tag as

UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(gestureHandlerMethod:)];
[yourGestureEnableView addGestureRecognizer:tapRecognizer];
yourGestureEnableView.tag=2;

and in your handler do like this

-(void)gestureHandlerMethod:(UITapGestureRecognizer*)sender {
    if(sender.view.tag == 2) {
        // do something here
    }
}