I don't have a mortgage on my primary residence and don't received a 1098. Where do I deduct my property taxes paid in 2018?

In the itemized deductions area:

Federal Taxes / Deductions & Credits / I'll choose what I work on / under Your Home is Property Taxes

You are prompted for this when you go through the normal Step-by-Step flow. You only have to navigate like the above when you skip past things that apply to you and reach the end.