If the system is asking you to input what your property taxes are, and they are not listed on your 1098 (because you do not have them "escrowed"), you can look up the value of the property online and that is going to be the "best effort estimate" you're making which is what the IRS requires you to make if you do not have the information (whether from 1098, receipts, cancelled checks, or the original town/county bill). Just put in the address of the property into any decent search engine - make sure it is pulling up that exact property address and not just one other random property on that same street, and whatever the estimated value is that is listed is what you can use.