That will be on your W-2 when you receive it from your employer. Employers have until February 1 to issue W-2's so you have to wait for it.
Every 2020 W-2 that you received must be reported on your 2020 tax return, even if they are for small amounts. Remember that each one of those W-2’s has your Social Security number on it, and that income was reported to the IRS by the employer. You do not want to get in trouble with the IRS for under-reporting your income.
ALL of your W-2’s must be entered on the SAME tax return. After you enter the first one, you click Add Another W-2.
W-2's come from your employer, and they have until February 1 to issue it. Some employers allow you to import the W-2 through the software, but for security reasons you still need information from the actual W-2 to import it. You might need to phone, drop in, email and/or snail mail an old employer to make sure they know where to send your W-2.
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What are you trying to complete? Your employer's EIN number can be found on your W-2 or paystubs.
If your business pays other employees, your business should apply for its own EIN. If you are self-employed, but do not pay other employees, you do not need an EIN and would use your SSN as your tax ID.