China Jilin got how many airport? How do I go there from Singapore?

As I know, there are three airports in the province.
You can fly from Singapore to Beijing first and transfer to another plane from Beijing Capital Airport to Changchun Longjia Airport. As the air tickets' price varies from time to time and I am not sure when you will travel this journey, the website below may help you with the flight schedule and price:
https://www.travelchinaguide.com/china-flights/