Police shot and wounded a 20-year-old man in Brooklyn Thursday when he fired at cops during an attempted drug bust, law enforcement sources said. The shooting came on the eve of the wake for Kimani Gray, the 16-year-old killed by police in East Flatbush on March 9, and less than an hour before a peaceful march in his memory.Two plainclothes narcotics officers believed they spotted suspect Shaquille Reid dealing drugs near Grafton St. and Livonia Aves. in Brownsville around 6:15 p.m. Thursday, police sources said. As the officers approached, Reid pointed a 9-mm. handgun and fired once at them, a source said. The cops returned three shots, with one bullet striking the suspect in his buttocks and another in his wrist , sources said.