Your employer is required to issue you a W2. You should contact them first and request your W2. You can also request a Wage and Income transcript from IRS.gov.
The Wage and Income Transcript - shows data from information returns we receive such as Forms W-2, 1099, 1098 and Form 5498, IRA Contribution Information. Current tax year information may not be complete until July. This transcript is available for up to 10 prior years using Get Transcript Online or Form 4506-T. here is a link Wage and Income Transcript
Please see the attached for additional details What to do if I don't have a W2?