About 20 years ago singer Youssou N’Dour, who stands at the top of modern Senegalese music, visited the island of Gorée near his home in Dakar. It was the start of a mission to trace the paths of the many Africans transported from there to the Americas and Europe as slaves, and to trace the paths of the music that emerged from the depths of those horrors — specifically jazz and gospel. The directive was for him, accompanied by Swiss pianist Moncef Genoud, to bring that music back for performa...