What is debt on data last secured mean and how do I fill it out?

[KrisD]

I think you might be asking about Home Mortgage Interest and that would be the amount of the loan on the date you took the loan out on the house. 

[jdambroise]

what if there is a 2nd mortgage that was taken out, what amount should it be?  the amount of which loan on which date?

[VictoriaD75]

Beginning in 2018, interest on a home equity loan or line of credit is only deductible if the loan was used to "buy, build or substantially improve" the home that secures the loan. You cannot deduct interest on a loan used to purchase a second home.

Home Equity Interest

You need to indicate the amount on the second mortgage that was used for this purpose.