Each state does 1099-G forms differently and they may not have the same corresponding box numbers as TurboTax. You can enter your SSN and the amount paid and then check the box for withholding.
If there is no designation, then the withholding is likely Federal (the rate would likely be withheld at 10% of your benefits paid). Also, if you live in either California, New Jersey, Oregon, Pennsylvania, or Virginia, then it is definitely federal withholding as those states do not tax unemployment benefits.
