Unless one of Western Digital's tools provides such a utility, you can't. Those tools must be run from a local operating system; they are not supported by typical network filesharing protocols.
The My World Book NAS is essentially a mini-server running a Linux OS (you can get the source code from WD). If the OS provides an SSH terminal interface, you could SSH into it and run standard Linux filesystem tools (fsck, mkfs, etc) there.
The Hacking WD MyBook World forum is a good resource for owners of this device. One post gives instructions on enabling SSH on the MBW:
If your firmware is version 01.00.14 or later, you can easily enable SSH without any hacks! Simply log into the web administrative interface.
- Click on the Advanced link in the upper right to enable more selections1.
- Select the System TAB
- Select Advanced ICON
- Now click on Enable SSH
- After SSH is enabled you can login as either 'admin' with the admin password (default is 'admin'). You can also login as root using 'welc0me' as the initial password.
- Once you have logged in as root, you can change the password from the default using the 'passwd' command.
- If you make other users in the web interface, they can log in via ssh, but must put their username in all-caps ("USERNAME" not "username").
Once logged in via SSH, you can run "fsck" and related tools. Here are some links from the Hacking MBW forum that might help you out: