It depends where you bought it and whether it was a download or CD. For instance, if you bought a download directly from TurboTax, the license code should be in the download section of your online account.
If you purchased a download from Amazon, the license could should be in the Digital Downloads (or Games and Software Library) of your Amazon account.
Also, if you ordered a download from someplace online, the license code may be in an order confirmation email.
If you installed from a CD or otherwise need assistance with the code, phone TurboTax Support and discuss the issue with them.
Support hours are 5AM-9PM Pacific (8AM-12 Midnight Eastern), 7 days/week
FAQ: What is the TurboTax phone number?
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632