schedule C needs a principle business activity code (6 digit code), where do I find this worksheet?

Business codes are used by the IRS to categorize your business for statistical purposes only. The code you enter won't affect the outcome of your tax return.   You can enter 999999 in that field to continue to your return.  

TurboTax Online

When inputting information about your business in TurboTax Online, TurboTax will automatically select your business code. Once you've input all the information for your business you can review your business information.

Go to Tax Details Business Code and select Edit.

Here you can select Look up my business code to verify the code is correct.  A list business categories will be shown, select the code that best describes your business and input it into the Business code box.

TurboTax Desktop

When you set up your business in TurboTax Desktop, you'll eventually come to the Let's look up your business code screen.

Select Lookup Business Codes and enter some keywords that describe your business (for example, day care, bookkeeping, or door-to-door).

Select the category and code that most closely resembles your business's activities. If you can't find a code that applies, you can enter 999999.