Box 16 on what form? A W-2? What state did you work in? If your state does not have state income tax, and box 17 is also blank, leave boxes 15, 16, and 17 empty in TurboTax. You don't need anything.
If there is an amount in box 17, but box 16 is blank, your W-2 is not filled out correctly. Ask your employer for a corrected W-2.
If you are talking about box 16 on a different form, tell us what form it is.