If your (and your wife's) W2 shows nothing in Box 2, then -- in theory -- it means the employer didn't withhold federal taxes. The question then becomes, is that correct?
When you received your pay stubs during the year, if you recall not seeing any taxes taken out, then the W2 is probably correct. But that's not a common situation. Normally for that to be the case, you'd have to sign the W4 form at work, stating "exempt" from federal taxes in Box 7).
This is something you should probably verify with the payroll person at work, just to be sure that the blank Box 2 is not an oversight and that there really were no taxes withheld. And if that is correct, then you'll want to change your W4 so this doesn't happen in 2017.
I looked at our pay stubs and it looks like they have not been taking out for federal taxes all year. I don't know why though we never filled out a W4 and they withheld them last year