How do I find out which w2 has the incorrect EIN number?

you have to go through them one by one 

In the search box type: W-2
click on Jump to W-2
On the W-2 summary screen, click Edit next to each W-2 on the return and make sure the EIN in Box b exactly matches what's on your W-2 form. If not, make the correction.

If you do not find your own typo as Mike9241 replied, look at a pay stub from each employer.  If it includes the EIN, you can compare each to the W-2 you got, and you may find the service issuing the W-2 made a typo.  Failing that, search the internet for the EIN on each W-2.  Most EINs are not posted, but you might get lucky.  Beyond that, you can call the employer or call a co-worker and ask them to verify the EIN.