Use the point of the exacto to probe straight into the pad. The hole is most always in the widest part of the pad. (see pic) Holes are also sometimes put under labels. Pressing on the label with your thumb can leave a circular indentation, reviling the hole location.

Once the void is found cut sideways till you find the perimeter of the hole, and trace around.

If there is no hole at the probe location you will know when you meet the additional resistance of the under laying plastic. This will leave a small pin prick of no account.