It is a natural desire to want to share something that has meaning and has been of benefit in your life—in this case, the study and recitation of Patanjali‘s Yoga Sutra. This is a profound and foundational text for yogic philosophy and practice. Traditionally, an aspirant learned and studied the Sutra from a teacher through shruti parampara, or call-and-response chanting. In this manner, over time, the mind’s focus improves and the terminology and ideas of yoga become familiar, their meaning revealed. Chanting the Sutra can be an exhilarating and vital aspect of a yoga practice.
As for whether a certification program exists—yes, for learning Sanskrit. There are any number of Sanskrit programs, and venues that offer certification upon course completion. Many of these include study of the Yoga Sutra. Whether there is a certification course for strict study of the Yoga Sutra only, I cannot say. There may be, but I have not heard of it.
Whether you can lead a study group without certification is up to you. Yes, if you feel confident, have the necessary teaching skills and qualities, and are competent and knowledgeable in the subject. If this is the case, certification is not required. Even without these attributes, certification is not required, but it might be considered improper. Being a sincere yoga practitioner with practical experience will greatly enhance your understanding of the Sutra and your ability to discuss and explain it to a group.
If your understanding and knowledge are ripe, then leading a group in chanting and exploring the Yoga Sutra will be a rich, rewarding, and enjoyable experience for both you and the group participants. Chanting the Sutra will help develop the philosophical tools needed to cultivate the mind of a yoga practitioner. If you feel ready, follow your calling. Or if you do not feel quite ready to lead such a group, you might enjoy starting an informal study group, not setting yourself up as a “leader” but making it a meeting of like-minded practitioners.