You should confirm with your Employer whether the 2nd W2 is a duplicate or if it reports additional income.  

If you know about what you made per week in gross wages or have a paystub, you should be able to get an idea of what your "total" wages should be for 2018.

You may receive 2 W2's from the same Employer when they change payroll processors; however, it is rare that the amounts on both W2s are exactly the same.