The question that asks if you contributed to a college savings plan established my MA (ie. MA 529 plan) appears on the Education Expense screen when you go through the state questions. (Click on screenshots below). Once you check the box next to Contributed to a college savings plan established by Massachusetts and click Continue, you will be given the box to enter the qualified contributions to the MA 529.
To get to the Education Expense screen if you have already completed the state interview questions:
1. Open your tax return
2. Click on the State Taxes tab and click Massachusetts
3. Click Update next to Adjustments (click on screenshot below)
4. Click through a several questions until you reach the Education Expenses question.
5. Check the box next to "Contributed to a college savings plan established by Massachusetts".