I work one job in two states. I file nonresident return in SC; resident return in GA. I work in GA 3 days/week; 2 days/week in SC. Can I apportion the wages betw the two?

Since South Carolina is your resident state, 100% of your income is taxable by South Carolina.  For Georgia, you should allocate 60% of you income to Georgia in the non-resident state tax return.  You won't be double taxed, as South Carolina will give you a credit for the tax you pay to Georgia.