I think that your problem is with this line:
wd = pluginHost.getWorkingDirectory(C:\xampp\htdocs\learn\doit)
The 'getWorkingDirectory' method returns a String, it doesn't take one as a parameter. I think what you want instead is this:
wd = "C:\xampp\htdocs\learn\doit"
However, note that Whitebox will update the working directory as you work with spatial data. This means that if you've recently opened a file for display in that directory, it'll already be set as the working directory.
The 'pluginHost' object (quite literally the Whitebox GUI) implements the Communicator and WhiteboxPluginHost interfaces and the details of the various methods belonging to these can be found here:
You may also want to see these tutorial on workflow automation and scripting in Whitebox: