Here is a blank 1040 return. You can see what adds up to the AGI on line 8b. https://www.irs.gov/pub/irs-pdf/f1040.pdf
Or do you need your 2018 AGI to efile 2019?
You need your 2018 AGI to efile 2019. The AGI is on 2018 1040 line 7. If you filed a Joint return you use the same AGI for each spouse How to find the AGI.
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947
