I want to efile but my w-2 doesnt have a box twenty it blank what should i do

Is there anything in box 18 or 19?  

Q. I want to efile but my w-2 doesn't have a box twenty it blank what should I do?

A. Enter something in box 20, at the W-2 screen, if there are entries in boxes 18 & 19.  

If there are entries in boxes 18 & 19, your employer has withheld local income tax.  Your employer should have identified the local taxing jurisdiction (City, county, school district, other) in box 20.  If they left it blank, type in the name of the taxing city.  You can use an abbreviation. 

If box 18 has an amount in it greater than zero, then boxes 18, 19 and 20 must have something in them. Period.
If box 18 is blank, or has zero in it, then boxes 18, 19 and 20 *must* be blank. Not even a space in any of those boxes.