In December, Trevor Noah, a 31-year-old comedian, made his debut as an on-air contributor on “The Daily Show With Jon Stewart,” offering his outsider’s perspective, as a biracial South African, on the United States. The network’s selection of Noah comes less than two months after Stewart, 52, revealed Feb. 10 that he was leaving “The Daily Show” after a highly successful 16-year run that transformed the show into authoritative, satirical comedy on current events. Noah, who spoke by phone from Dubai, where he is on a leg of a comedy tour, said he had been given a great opportunity, as well as a significant challenge. The appointment of Noah, a newcomer to U.S.