The EIN number is actually your "employer's identification number" and you would need to obtain that from either your employer or your W-2. If you cannot find that information or cannot obtain a copy of your W-2, you would need to obtain the information from the IRS, via a "tax transcript".
You can order your transcript from the IRS Get Transcript by Mail service or by calling their toll-free number 1-800-908-9946.
Failing to obtain a copy of your W-2 may result in an additional assessment or your return being rejected if the information is incorrect.
