If you are needing your 2017 AGI amount to verify your identify to file your tax return, using an old W-2 form will not help. You will need the AGI amount from your 2017 tax return. 

If you do not have access to your prior year return, you can request a free online transcript of your 2017 tax return from the IRS.  The transcript will include your 2017 AGI amount on it.  Use this link:  IRS Get Transcript

Below is more information on where to find your 2017 AGI on your prior year tax return:

 https://ttlc.intuit.com/replies/3301618