If a CSF 1099R form is fill out in box 2a Taxable mount as UNKNOWN. Does the mean the survivor annuity paid is not taxable?

No it does not mean that the survivor annuity is not taxable. This means that OPM did not calculate the tax-free portion of your annuity. You can leave the taxable amount box blank and TurboTax will guide you through the interview to determine the taxable amount