First, ask the person who prepared your taxes if they have your AGI from last year. If they did not keep a record and you do not have a record yourself (even a paper copy would do) then you can request a transcript from the IRS. I had a computer crash one year and lost my records but the IRS will not lose it. Here is a link, hope it works for you:
https://www.irs.gov/individuals/get-transcript
