Are you trying to deduct the mortgage interest paid on your second home? If so, you are looking for the Form 1098 mortgage interest section.
Here's how to make these entries in TurboTax Online:
1) In TurboTax Online, enter 1098 into the search field (magnifying glass) in the upper right of your screen.
2) Select the Jump to 1098 button. Follow the guided interview to make your entries using your 1098 you received from your mortgage lender.