After you file

@Lora21 is correct, but you may be able to import you W-2.

Please see the TurboTax Article What To Do If You Haven't Received a W-2

You may be able to import you W-2 with TurboTax Online

You will need your employer's tax ID number.

You may be able to get this from a previous year.

1. Sign into TurboTax

As an alternative you can go to the main menu.

1. Select Tax Tools
2. On the drop-down select Tools
3. There will be 4 green boxes
4. Select Topics Search
5. Type Import W-2
6. Select Work on my W-2 and Continue. 
7. If you've already entered a W-2 or need to add another one, select Add another W-2.
8. Enter your Employer Identification Number (EIN) from Box b on your W-2.