Seek that from the former employer(s). Or seek a work history from Social Security.
WORK HISTORY https://www.ssa.gov/forms/ssa-7050.pdf
That depends on what kind of proof you actually need.
If you filed using Turbotax online, you should be able to download a PDF of your tax return. That will show your income, and there will be a "W-2 worksheet" that shows the information copied from your W-2, although it is not a legal copy of your W-2.
Or, you can log into your IRS online account and get your 2019 and 2020 tax return transcript, this is a summary of your tax return that is usually acceptable for getting loans and other purposes. It will show wages, self-employment income, your deductions, and anything else on your tax return. (Of course, it only shows what you reported to the IRS, so if you also worked under the table, it won't be on your tax return.)
https://www.irs.gov/individuals/get-transcript
You can also log into your social security online account and see your income records (income that was reported to social security and subject to social security tax.)
Lastly, you can request an actual copy of your W-2 from the social security administration, but that costs $126.
https://www.irs.gov/faqs/irs-procedures/copies-transcripts/transcript-or-copy-of-form-w-2