What would you say to this Laowai?
By raising and resting his feet on top of the backrest of the front passenger seat, his behavior is clearly disrespectful to fellow train passengers. There's also a chance that he might be intoxicated. So, it's unlikely that I'll bother myself to personally ask him to put down his feet.
There are 2 ways to best deal with that situation:
First is call a train conductor. Let them know the situation and politely ask if it's possible to let you seat elsewhere. Since the trip from Shenyang to Beijing is at least 6-hours long, that would be uncomfortable knowing someone with socially undesirable behavior sitting behind you.
Second is to request the train personnel/police to impose passenger rules of conduct.