If I don't have my 1040, can I still use the 8879 to confirm AGI?

[Trevor N]

Yes. Since Form 8879 pulls the AGI value from Form 1040 it should work as long as it was the final version from the original filing. You can find your AGI on Line 1 of Part I.

You can read below about where to find your AGI.
https://ttlc.intuit.com/replies/3301618
How to get a copy of your return if you did use TurboTax Online:
https://ttlc.intuit.com/replies/3301525
If you didn't use TurboTax Online to file last year (and/or you don't have a copy of your return) then you'll need to request transcripts from the IRS or file by mail:
https://ttlc.intuit.com/replies/3301999
https://ttlc.intuit.com/replies/4170366
If you did, but can't access your TurboTax Online account or your prior year data isn't showing up in your account, then read below:
https://ttlc.intuit.com/replies/5667209