Are you looking for 2019 AGI? You need your 2019 AGI to efile 2020. The AGI is on 2019 1040 line 8b. If you filed a Joint return you use the same AGI for each spouse.
How to find the AGI.
If you didn't file 2019 or filed it later in the year then try entering 0 for the AGI. If that doesn't work you will have to print and mail your return.
Or request a transcript from the IRS
Or did the AGI reject? When did you file 2019? If it was late in the year or you mailed it, try putting in 0 (zero) for the AGI. And see, https://ttlc.intuit.com/community/rejections/help/what-if-i-entered-the-correct-agi-and-i-m-still-ge...
How to correct the AGI
If you can’t get it to efile you will have to print and mail it.
How to mail a return from the Online version
Be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.
For AGI Reject code 031