I sold our two rental house in 2017, and didn't claim the depreciation in the previous years. I know it should recapture when I sold them, turbo tax asks the amount taken in prior years, do I enter 0? or enter amount I should have taken? thanks.
You would enter the amount you should have taken. I also suggest you file Form 3115: Application for Change in Accounting Method to try to recoup the past depreciation not taken. Please read more about it at this link.