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
    }
}

Here is an update for Swift 3 and an addition to Mani's answer. I would suggest using sender.view in combination with tagging UIViews (or other elements, depending on what you are trying to track) for a somewhat more "advanced" approach.

  1. Adding the UITapGestureRecognizer to e.g. an UIButton (you can add this to UIViews etc. as well) Or a whole bunch of items in an array with a for-loop and a second array for the tap gestures.
    let yourTapEvent = UITapGestureRecognizer(target: self, action: #selector(yourController.yourFunction)) 
    yourObject.addGestureRecognizer(yourTapEvent) // adding the gesture to your object
  1. Defining the function in the same testController (that's the name of your View Controller). We are going to use tags here - tags are Int IDs, which you can add to your UIView with yourButton.tag = 1. If you have a dynamic list of elements like an array you can make a for-loop, which iterates through your array and adds a tag, which increases incrementally

    func yourFunction(_ sender: AnyObject) {
        let yourTag = sender.view!.tag // this is the tag of your gesture's object
        // do whatever you want from here :) e.g. if you have an array of buttons instead of just 1:
        for button in buttonsArray {
          if(button.tag == yourTag) {
            // do something with your button
          }
        }
    }
    

The reason for all of this is because you cannot pass further arguments for yourFunction when using it in conjunction with #selector.

If you have an even more complex UI structure and you want to get the parent's tag of the item attached to your tap gesture you can use let yourAdvancedTag = sender.view!.superview?.tag e.g. getting the UIView's tag of a pressed button inside that UIView; can be useful for thumbnail+button lists etc.