How does an apartment verify w2 if you are a small business owner? Who do they call? ?

You'd be asked to show your tax return.

If you own a small business, you have no W2 forms to be verified. In that case, you could submit a copy of your tax return to the apartment in order for them to verify your income.

Business owners don't HAVE W-2s.

People checking income require actual business records and/or tax returns.

If you own a small business you won't HAVE any W2 forms. Instead, you will have bookkeeping and proof you own a business--such as a business license, and records of your income and expenses. They can't "call" anyone to verify something that doesn't exist. 

Sole proprietors do not receive a W-2.  You would need to provide a copy of your tax return.  A transcript of your return from the IRS and/or a letter from your accountant might also be requested.

They would probably require additional info such as the business tax return, which would verify

they might call a tax place

They will know whether it is fake or not and they would call your employer to verify, if they wanted to.

maybe a tax place

They have to trust you.