What do I do when my 1099R form says unknown in box 2a (taxable amount) and also in box 9b (total employee contributions?

When the taxable amount isn't reported (Unknown), TurboTax gives you the option to use the Simplified Method to determine the taxable amount of your distribution. 

Return to the entry screen for your 1099-R and when you go through the interview, TurboTax will ask you questions about your 1099-R so you can use the Simplified Method.

1. Navigate to the 1099-R section:
   • TurboTax Online/Mobile: Go to 1099-R.
   • TurboTax Desktop: Search for 1099-R and select the Jump to link.
2. On the Your 1099-R screen, select Yes and then Continue.
   • If you land on the Your 1099-R Entries screen instead, select Add Another 1099-R

Review the TurboTax article Where do I enter my CSA 1099-R? for more information.