As long as you're considered active duty, your military pay can only be taxed by your military SLR (State of Legal Residence). If you take a side civilian job while still on active duty, that income would be taxable by the state in which you perform the civilian job.
After you separate from service, your income is taxable by your new civilian State of Residence. If you work in a state other than your new State of Residence, then your income would also be taxable by the state in which you perform that work. In that scenario, you'd be able to claim a credit on your resident state return for the taxes paid to the non-resident state, so you wouldn't be double taxed.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
