Ahmir “Questlove” Thompson on how sifting through 40 hours of archival footage of the 1969 Harlem Cultural Festival — where legends like Nina Simone and Stevie Wonder performed in the same summer as Woodstock — led to his debut documentary, ‘"Summer of Soul.” Plus, how the parallel protests of 2020 and 1969, as well as a focus on Black joy, helped to shape the film, and why he still considers "The Tonight Show" with Jimmy Fallon his creative epicenter.