Not working in linux mint serena either:

Running Planescape: Torment Enhanced Edition
./Torment: error while loading shared libraries: libjson.so.0: cannot open shared object file: No such file or directory

Installing libjson.so.0 through apt has no effect.

EDIT: I fixed this by creating the following soft link:
sudo ln -s /lib/i386-linux-gnu/libjson-c.so.2.0.0 /lib/i386-linux-gnu/libjson.so.0

Almost 1am and I have work in the morning, but enjoying it so far. Played it through back in the day and it's nice to revisit. Had the issue on Linux Mint with libjson.so.0 missing but installing the libjson0 package and doing an updatedb fixed that for me.