There is an Underpayment Penalty section in the California interview; it may not appear unless TurboTax has calculated a tentative penalty for California.
In that case, you will see Underpayment Penalty listed as an item under Other Situations in the California interview. You may also see a screen prompt before you get to the end of the California items asking if you want to go over the penalty section now. Respond "yes" to "Would you like to review this topic?". If yes, you are given the choice to let the Franchise Tax Board calculate the penalty and send you a bill, or to complete the questionnaire.
See this FTB webpage for more information about California penalties.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"