If you can't get your W2 then you can check your account at the IRS to get the information that was filed. You will create an online account and then take a look at your 'wage and income transcript'. That will have information on everything that the IRS has received with your information on it for the year.
Go here to create your online IRS account.
If that doesn't have your W2 in it then you can contact the IRS directly (prepare for long waits on the phone) and file form 4852 with your return.
Here is some more information on these steps.
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