1 You can use your testimony if you are a credible witness, this can prove the employer-employee relationship.2 Check- or paystubs if you were paid by them, you should have a record of it, and being paid will establish employment. This applies also to records of direct deposit.3 Testimony by  co-workers, who can testify you worked there.4 Security records from the building, if applicable, which may show you entered there so regularly as to be an employee.5 Emails or other correspondence from the empoyer to you. This includes text messages.6 Testimony from customers or clients who know you worked for this employer.