You pretty much always can find the location of a properly installed piece of software with the command "whereis", in this case meaning "whereis openxcom". However, the place of the data-folder is somewhere else. You can see the paths, openxcom is looking in for it, in one of the logs in the folder ~/.local/openxcom/. There is also one path not logged, inside users home folder. I just forgot its name... But by this means, every user can have his own version of data, with own selection of mods 'n stuff like that.