Figure out how to hide it. Ask it to tell me how it got to Earth so that humans can reverse engineer the technology and start to explore the galaxy. Ask it why its species have evolved to be completely green. Ask it to describe its home planet and native culture. Ask about its family. Ask it how it knows English. Ask it how its immune system is coping with Terran microbes. Ask it how the government managed to capture a member of a species that has the technology to traverse interstellar distances. Ask if it wants to return home - if its spacecraft is still functional, if other members of its species are on their way to rescue it, etc. Ask if it needs any food or drink, and if it has any special dietary requirements, because I don't want to accidentally poison it with Earth food. Ask it if I can answer any questions about Earth's biosphere, human anatomy or culture, or any other topic it's curious about.