How do I know if turbotax is not counting my 1099-MISC Nevada income (state-tax free) as South Carolina state taxable income? I live in SC but one job is in Nevada

Typically, when you are entering income in more than one state, you will allocate between the separate states using two TurboTax state programs.  Since there isn't a Nevada TurboTax program, you will need to make a manual adjustment as follows:

1. Click on State on the left side of the TurboTax menu.
2. Continue until you see the screen Here's the income that South Carolina handles differently.
3. Click Start (or Revisit) beside Other Subtractions.
4. Type Income Earned in Nevada in the Description box.
5. Enter the amount of income earned in Nevada as a positive number in the amount column.  This number is subtracted from your South Carolina income.  

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.