Where can I find the State distribution for Box 16?

Box 16 of what, exactly?  We cannot see your screen or your tax return.  There are a lot of boxes --- what are you working on?

@ddpm-yuvn-62ch-n 

Maybe box 16 of a 1099-R form?

If so, then it's usually the same as box 2a of the 1099-R form....IF b0ox 2a has a real value in it.

IF box 2a is empty (or 2b is checked as "undetermined"), then it's the Federally-taxable amount from box 1 (which is usually just the box 1 value).