Hi,
It would be listed on Form 6251 ("Alternative Minimum Tax-Individuals").
You should look through all your prior years' returns for all the years you owned the property. You will have to look at each form 6251. Make a list of all the years and the amounts for each year.
For 2017, it was on line 18 (it's called "depreciation on assets placed in service after 1986 (difference between regular tax and AMT)".
It would be very similarly called (if not identical) on other years' Form 6251's. It should be around Line 18 as well.
hope that helps!
