Could you clarify what PIN are you referring to? The IRS IP PIN (Identity-Theft Protection PIN number) which is a 6 Digit PIN issued every year by the IRS for you to file electronically, or the 5-digit TurboTax PIN, which is a number you created as a signature.
If you need the IP PIN, you should have received a letter from the IRS with the PIN included. If you didn't receive the letter, you can create an account on the IRS website (if you don't have one) to retrieve it. See the link below:
Get an identity protection PIN (IP PIN)
If you need the PIN to e-file your tax return, you will need either last year's self-created 5-digit PIN, or last year's AGI (adjusted gross income). Your 5-digit PIN isn't saved anywhere; in this case you can use you AGI instead. Your last year AGI is located within your prior-year tax documents Form 1040, Line 11.
How do I find last year's AGI?