You are asking about desktop but tagged as Online. Desktop 2019 certification are accessible from your pro advisor account AFTER paying $349 annual pro advisor fee.

If you instead are asking about the free online pro advisor program there is no 2019 program as it is not yet 2019. Program details https://quickbooks.intuit.com/accountants/proadvisor/?cid=ppc_G_e_US_.ASG_US_GGL_Brand_Core_Exact_Se...