Shanghai to Hong Kong Train
Having said that, I found the Chinese sleeper trains to be surprisingly comfortable. There are, however, several different classes. The Wikipedia article on your train has details on which classes are available. (Side note: Chinese trains in general surprised me. The Shanghai-Suzhou train was actually more comfortable/modern than a recent German ICE.)
While I didn't take this particular train, I experienced both a "soft sleeper" and a "hard sleeper" on different routes (Nanjing-Zhengzhou and Zhengzhou-Taiyuan, respectively). Soft sleeper basically means you can shut a door and beds are fairly comfortable. Hard sleeper aren't as hard as it sounds, but they can be quite crammed (in my case, three beds stacked vertically) and since they are open to the aisle there's next to no privacy.
However, this was still okay for me for one night. This is probably as bad as it gets.
Now compare this to the pictures in the mentioned Wikipedia article. I envy you already! That train looks really modern and comfortable.
As for "doing some activities", if that means doing concentrated work, I wouldn't expect to be able to do that. Reading a book, looking outside, playing a card game with some kids, sure.
In conclusion, Chinese sleeper trains are actually quite comfortable and I would recommend travelling with them as it can be a great experience! The only thing you should plan well is getting the ticket, since there are times when they are sold out really fast. Maybe someone can elaborate on the situation on this particular route.