The One and Only Ivan by Katherine Applegate

Having spent twenty-seven years behind the glass walls of his enclosure in a shopping mall, Ivan has grown accustomed to humans watching him. He hardly ever thinks about his life in the jungle. Instead, Ivan occupies himself with television, his friends Stella and Bob, and painting. But when he meets Ruby, a baby elephant taken from the wild, he is forced to see their home, and his art, through new eyes.