Getting from Ji'an to Changbaishan (Baihe or Songjianghe)?

You should refer to Erdao Baihe. I remember there is bus service from Ji'an to Baihe, but not very sure, which requires ur further consultation. Upon getting to Ji'an, you can rent a car or transfer to a shuttle bus to Changbaishan.

Or there is direct tourism train service between Ji'an and Changbaishan. It leaves Ji'an at 09:00 and returns from Changbaishan at 10:25. You can buy the ticket and catch the train at Ji'an Train Station. I took the train in 2012, so you'd better consult further if it is still available.