It depends on how you filed them. If you filed a paper copy and don't have it any longer you can request a copy of your tax transcript from the IRS:
https://ttlc.intuit.com/replies/3301999
If you filed it with TurboTax online then follow these directions:
https://ttlc.intuit.com/replies/3301525
If you are looking for it on your computer because you used TurboTax CD/Download software for Windows follow these instructions:
https://ttlc.intuit.com/replies/3301497