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

A penalty has nothing to do with it.   The 2018 AGI is the same regardless and can be found as VolvoGirl indicated.