Are you confused? It does ask for your 2019 AGI so that you can e-file 2020. But that is not on your W-2. Your 2019 AGI is on line 8b of your tax return---your 2019 Form 1040.
Your 2019 tax return shows your 2019 Adjusted Gross Income (AGI) If you filed a joint return then the AGI is the same for each of you.
Form 1040 line 8b