How can I find or search through Net Properties in xPCB?

There's Layout Automation Reference and Tutorial which should be accessible from Xpedition Layout's Help menu (try Help > Contents).  Additionally, get VbsEdit and install it on same pc as Xpedition Layout and create a .vbs file with following statement (it's commented):

Set pcbApp = CreateObject("MGCPCB.Application")

On the right side inside VbsEdit you should see an Object Browser, which will show you all objects and their properties and methods.  There's a Net object, which can be expanded to view all its properties/methods.

In xPCB, a Component object has a Properties property, but a Net object does not.  So, if you want to access the Net Properties found in xDX from xPCB, the best suggestion would be to write out that information from xDX to a file, then access that information in xPCB by reading the file.