You will have to get a statement from your county, town, or other local taxing authority. The 1098 statement from your mortgage lender should show the amount of tax they paid, but that is not necessarily the amount you can deduct.
You can deduct real property taxes you pay for property you own, but only for items that are of general community benefit. For example, if you are charged $4000 in general taxes and an additional $100 for upkeep of streetlights on your street (and homes on streets without lights don't pay this extra charge) then your property tax deduction is $4000 even though you paid $4100.
Only your local taxing authority can provide these detailed statements to you.
You do not get an IRS form (e.g 1099) for property taxes paid. You get that information from your own records (usually the invoice from the property tax authority).
If you pay your proerty tax to the mortgage company, they may include that info with the 1098 they send you; but they are not required to do that.