Where do I enter the gross distribution on a 1099Q ?

It is entered under Wages & Income, Less Common Income, Miscellaneous, but only if it is taxable.   If you know that the distributions from the 529 plan are not taxable because they were used on qualified expenses, do not enter the 1099-Q forms.  For most qualified education program beneficiaries, the amounts reported on the 1099-Q aren’t reported on a tax return.   Keep the form and associated education expenses with your tax records.

If the distribution doesn’t exceed the amount of the student's qualifying expenses, then you don't have to report any of the distribution as income on your tax return. If the distribution exceeds these expenses, then you must report the earnings on the excess as "other income" on your tax return. When you pay a student’s school expenses with these funds, you cannot claim a tuition deduction or either of the educational tax credits for the same expense.

Room and board usually isn't considered a qualified education expense for the purpose of education credits.  The one exception is if room and board was paid for with a Coverdell ESA or 529 plan distribution.   In that case, the cost can be deducted from the taxable part of the plan's distribution.

If taxable, it goes to Miscellaneous; see below: