Fill out the SAQ-EP if you are a normal self hosted ecommerce site that outsources their payment to a 3rd party. Self Assessment Questionnaire (SAQ).
SAQ A vs. A-EP: What E-Commerce Merchants, Service Providers Need to Know Now
Worth noting that others may interpret this differently:
Just fyi (shameless affiliate link coming up), WPEngine host is PCI Compliant “as long as no payment card data is stored, hosted, or otherwise processed by WP Engine…”