What novel did the quote that Harlem was a “dreadful place…a kind of concentration camp, where at the age of ten he was beaten by two police officers because of the color of his skin” come out of?

The quotation comes from Sonny's Blues by James Baldwin. It gives you some idea of just how hard life could be in Harlem at that time. This is a place of poverty, a place of hopelessness and despair. What's more, it's a place where racism is rife, as the overwhelmingly African American population regularly encounters abuse at the hands of white police officers.
To make matters worse, Harlem seems like a concentration camp in that it's a place from which there's no real escape. Even Sonny's brother, with his relatively well-paid job as a teacher, can't quite escape the continued hold that Harlem has on his mentality and his sense of identity. As for Sonny himself, his chosen method of escape is to pursue a life of crime: selling heroin, to be precise. This is the only way he feels he can be somebody in this rough, dead-end neighborhood. But as he'll soon discover, his criminal activities will simply bind him more closely to Harlem than ever before.