Are you referring to box a on the W-2? This is your SSN (or at least, it's the SSN of the person whose W-2 it is). In this case, just enter the correct and complete SSN.
But if you are referring to box b, this is the employer Employer Identification Number. You can call your employer and ask what it is; they have no reason not to give it to you.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"