Why do some people have a hole on the top of their ear?

Ok first let's get past the obvious answer which is a piercing with no jewelery in it. Now I think you might be talking about the little hole some people have where the ear attaches to the jaw/skull. This is called a preauricular sinus. Those are harmless but do need to be watched because there could be discharge that builds up that will need to be drained and in more severe cases an actual cyst could develop that needs to be surgically removed. It's actually a birth defect where the skin doesn't completely attach which leaves a hole... Hope that helps! (If you want more info on it, google 'Preauricular Sinus'. Pictures will also pop up of it if you google image it...)