How to differentiate whether a user is tapping the screen with his finger or an apple pencil?

To check if a UITouch is using the stylus touch type in Objective-C:

if (touch.type == UITouchTypeStylus) {
    // Do stuff
}

If you're not handling touches directly, but using a gesture recognizer, then it is a little more complicated.

You could try adding a second long press gesture recogniser and setting the allowedTouchTypes property on each one to recognise stylus or direct touches:

longPressGestureFinger.allowedTouchTypes = @[@(UITouchTypeDirect)];
longPressGesturePencil.allowedTouchTypes = @[@(UITouchTypeStylus)];

If that doesn't work, you would have to add a delegate to the long press gesture, and in the gestureRecognizer: shouldReceiveTouch: method, check and store the type of touch and use this when the gesture action fires.