It does not matter that you earned the income in NV. It is taxable on your SC return. There is no allocating to do.
The general rule is: your report all your income on your home state return, even the income earned out of state. You file a non-resident state return for the state you worked in and pay tax to that state. Your home state will give you a credit, or partial credit, for what you paid the non-resident state. The fact you happened to work in a state without an income tax, does not get you out of paying state income tax on that income.
