How do I get proof of income from 2019

Your proof of income is the W-2's you received from your employers and any Form 1099's that you received which includes income from the Payee.

Your proof of income would be the various income documents such as a W-2 Wage and Tax Statement from an employer, a 1099Misc from somewhere that you worked as an independent contractor, various other 1099's -- of which there are about two dozen types available from your banks or other financial institutions, etc.

What are you trying to do?

How can I get proof of income if I didn't work for whole year

@Jppp 

What income did you have?  Did you receive retirement income?  Disability?  Unemployment compensation?  Rental income?  Investment income?  What are you trying to do?

If you have to prove your income to someone like a landlord  then maybe an income transcript would be what you need ... https://www.irs.gov/individuals/get-transcript