Where do I enter the non tax deductible IRA contributions I made over the years to determine the actual taxable distibutions from my IRA?

After you enter the 1099-R for the distribution continue thru the follow up questions where it asks for the basis amounts from the prior year form 8606.... just go slow & read every screen. 

To reach this follow-up, be sure to click the Continue button on the Your 1099-R Entries page.