If your W-2s are identical down to the last number
and letter, you can either keep the duplicate with your tax records or
securely destroy it. Don't enter them both.
If one of your W-2s is mostly blank, just enter the other W-2
and make sure you include the info from the mostly-blank W-2. Usually,
"blank" W-2s have additional Box 12 line items or entries for a second
state in Boxes 15-20. Don't enter a separate W-2 if Box 1 is empty, as
you won't be able to e-file.
Otherwise, if each W-2 has different Box 1 amounts
which more or less add up to your yearly earnings at that job, enter
each W-2 separately. You might get more than one W-2 if your employer
switched to a different payroll provider or was taken over by another
company, or if you worked at different jobs through the same agency.