Do you want your 2019 AGI --- or your 2018 AGI so that you can e-file your 2019 return?
Your 2019 AGI is on line 8b of your 2019 Form 1040.
It it is really your 2018 AGI you want it is on line 7 of your 2018 Form 1040.
Where do I find my AGI?
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947
Your 2018 tax return shows your 2018 Adjusted Gross Income (AGI) If you filed a joint return then the AGI is the same for each of you.
Form 1040 line 7
If you are using the same TT account that you used last year, you should also be able to find this number in your Tax Home for 2018