This is the amount of Depreciation that you have taken on the rental, for the entire time you've had the property. If you have worksheets from filing your taxes somewhere else last year, you should have 'depreciation worksheets' attached to the back of your return.
Your depreciation worksheets will have an amount called Accumulated Depreciation, which is the total depreciation taken on your property to date.
Otherwise, if you filed within TurboTax in the past, you can report your property sold from within your rental basic info/profile and the Asset/depreciation section.
