1) contact the employer
2) obtain a transcript from the IRS - free - no state data
You'll need to create an account to access online
https://sa.www4.irs.gov/secureaccess/ui/?TYPE=33554433&REALMOID=06-00008e4d-63f6-1187-a229-7c2b0ad00...
or file form 4506-t for transcript - free
https://www.irs.gov/forms-pubs/about-form-4506-t
or file 4506 for copy by mail $43 fee
https://www.irs.gov/pub/irs-pdf/f4506.pdf
3) obtain an actual complete copy from Social Security Adm - $126 fee
https://faq.ssa.gov/en-us/Topic/article/KA-02501
