I think you want something like this....

If your original WoW folder is in your Applications folder and lets say you made a new folder in the Applications folder called "World of Warcraft 2" for your linked second copy.

ln -s /Applications/World\ of\ Warcraft/Data/ /Applications/World\ of\ Warcraft\ 2/Data

and

ln -s /Applications/World\ of\ Warcraft/WTF/ /Applications/World\ of\ Warcraft\ 2/WTF

make sure to include the backslashes as they are required to pass the spaces in the terminal.

Hope this helps