Since your son is a resident of NC, he will need to file a NC resident tax return. You are correct; he does not need to file a TN tax return. However, he does need to report the TN income on his NC return as well as any income he may have made in NC.
Since TN is a non-income tax state, he will not be able to claim a credit in TN for the TN income he reports on the NC return.
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