A Vincent van Gogh painting not shown publicly for more than 60 years recently drew hundreds of people to Sotheby’s Hong Kong. Painted in May 1890, Châtaigniers en fleurs (Chestnut Trees in Flower) is a major work from his Auvers-sur-Oise period and could set an auction record. For three days, Sotheby’s opened the private collection to public viewing in Hong Kong. Its brief stay raises a question about the city’s art hub ambitions: what lasting expertise can be built around a masterpiece that...