The title certified sexuality educator, or certified sex educator, is a private, non-government designation that has no national or international standard. There are a few international organizations (like the American Association of Sex Educators, Counselors, and Therapistst) that certify sex educators. There are also smaller schools, organizations, and professional groups that offer certification programs. But there is no consistency across organizations and someone who is an AASECT certified sexuality educator may have very different qualifications from someone certified in Canada by a regional sexual health organization.
What this means is that someone who says they are a certified sexuality educator isn’t saying very much without telling you more. They need to explain where they got their certification, what was involved in the process, what are the ongoing training requirements for them to keep their certification, and does their organization have a way for individuals to complain if they believe the educator is working unethically.
Most (but not all) certified sexuality educators will have had to take courses on different aspects of human sexuality and received training and supervision while working as a sex educator. Few certification bodies have exams that educators have to pass before becoming certified.