(Estou assumindo que sua pergunta é sobre os regulamentos da FAA.)
Se você já tem uma PPL, os requisitos são modestos. De acordo com a Soaring Society of America :
Additional Pilot Rating
Holders of a valid FAA Power plane license with 40 hours as pilot-in-command need a minimum of 10 solo flights to qualify to take the glider flight test. No written exam is required to add a glider rating to a power license. In all cases, refer to the Federal Aviation Regulations for details on pilot licensing.