Where do I find my active duty income to deduct to mo taxes

If you were in Missouri for 30 days or more you will have to file a resident return:

1. Start your Missouri State return
2. Select "Yes" on "Missouri Duty Station" screen 
3. Continue through the interview until you get to the "Active Duty Pay Deduction" screen and enter your Active Duty Pay

If didn't spend more than 30 days in Missouri and maintained a residence outside of Missouri then you are considered nonresident.

1. Start your Missouri State return
2. Select "No" on "Missouri Duty Station" screen 
3. Continue through the interview until you get to the "Active Duty Pay Deduction" screen and enter your Active Duty Pay (if you didn't have any other Missouri income and no withholdings then you won't get this screen).

Please see MO Military Guide for additional information.

But if you are eligible to get the deduction, the $ amount to deduct would be in box 1 of your  DFAS W-2.