As a general rule, income that you earn in another state is taxed by that state. All of your income is taxed by the state that you live in. One of the states will give you a credit for tax that you pay to the other state. If you tell us what state you live in and what state you will be testifying in, we can give you more specific information. Every state has different rules.
Will you be paid as an employee (you will get a W-2) or as a self-employed contractor (you will get a 1099-NEC, 1099-MISC, or no tax form)?
