You need to get the W-2 for this job. You'll end up getting a notice from the IRS that the income you reported on your tax return does not match the information in their records. The employer is obligated to make every effort to send the employee their copy of the W-2. I would contact the old employer and ask for a copy. Also, the following link is to the Social Security Administration and it may provide more information on how to get another copy of your W-2:
https://faq.ssa.gov/link/portal/34011/34019/Article/3836/How-can-I-get-a-copy-of-my-wage-and-tax-sta...
