That screen only asks if there is basis in the inherited IRA, not how much basis is in the inherited IRA. The purpose of that question is to prompt you to do the pro rata calculation on a Form 8606 outside of TurboTax and enter the resulting taxable amount when you answer Yes to this question. TurboTax has no ability to actually track the basis in the inherited IRA or to do the pro rata calculation for the inherited IRA, so that must be done outside of TurboTax.
