When you have indicated that the Form 1099-R being entered is from an inherited IRA, TurboTax will only ask for the taxable amount if you indicate during the entry of this form that the participant had nondeductible contributions. Note that online TurboTax mistakenly asks if you had nondeductible contribution rather than asking if the decedent whose name you entered had nondeductible contributions, so answer this question as if TurboTax had asked correctly.
If the decedent had no basis in nondeductible traditional IRA contributions, the entire distribution from the inherited traditional IRA is taxable.
