You get a miscellaneous deduction for the $11,000 loss, not a capital loss. You are entitled to report this loss only if you had a zero balance in all Roth IRAs on December 31, 2016.
If you received a Form 1099-R, enter it on TurboTax's 1099-R form, answer the follow-up questions, click the Continue button on the Your 1099-R Entries page, then answer the additional follow-up questions. Pay particular attention to the amount shown as your Roth conversion basis and your answer to the question asking if you had any Roth IRAs "open" on December 31, 2016 (had a zero balance in all Roth IRAs on that date). TurboTax will automatically report the miscellaneous deduction on Schedule A line 23.
If you received no Form 1099-R but otherwise met the requirements indicated above, you'll have to explicitly enter the deduction for Schedule A line 23.