VARANASI—Supriyo Maitro is an A-graded vocalist in the most ancient tradition of classical Indian music, “Dhrupad.” He has sung on the television and on the radio, performed before large audiences, yet he hasn’t experienced what the best in his field have described in the tradition—a divine path that seekers call “sadhana” in India’s yogic traditions. Sadhana simply means the cultivation of one’s spirit for self-realization, and Dhrupad, whose origin can be found in one of the oldest scriptures, the “Sama Veda,” has been used as a meditative tool. For Indian musicians like Maitro who want to keep learning after having learned everything, this aspiration for self-realization—for improvement in his spiritual cultivation—is natural. It’s this wish that brought him to the ghats (banks) of the Ganges in the ancient city of Kashi, also known by the modern name of Varanasi. Kashi, an ancient city of paradoxes, where people have been coming …