I can not get a w-2 from a former employer even after asking multiple times. What do I do?

You have a couple of choices.  

One option is to make your best estimate of your earnings and include it on your tax return using the substitute W-2 Form 4852.  However, using this approach will require you to mail your tax return since it cannot be electronically filed.

Your other option is to file your return without the missing W-2, request an Wage and Income Transcript from the IRS sometime after July when the records should be updated.  Then, file an amended return to include the missing W-2, assuming that it was reported to the IRS and shows in your transcript.

Use the links below for more information:

How do I file a substitute W-2 using Form 4852?

IRS - Get Transcript