A living monument to the Golden Era of Jazz, Clark Terry—a mentor to Miles Davis—is among the few performers ever to have played in both Count Basie’s and Duke Ellington’s bands. In the 1960s, he became the first African American staff musician at NBC, on “The Tonight Show.” Terry worked with and taught some of the most important figures in jazz history, and he continues to attract and cultivate budding talents, including the preternaturally gifted Justin Kauflin, a blind, 23-year-old piano prodigy who suffers from debilitating stage fright. Kauflin and Quincy Jones talk about their friendship with Terry, and the documentary “Keep on Keepin’ On,” shot over the course of five years by filmmaker Al Hicks. It opens Oct. 3 at the Landmark Sunshine Cinema and Lincoln Plaza Cinemas.