I was asked to do master suracing as a tooltest during an interview .
I am unsure what you mean by "master surfacing", one master may be another ones slave. It usually takes a combination of training and experience to master surfacing, I should know, I teach surfacing!! You can learn the tools, but you also need to learn where which tool is best used in what situation.
You can see what training course we deliver if you prefer at www.intrinsys.com
"master surface" is not a CATIA-specific term, but several companies (such as Boeing) that use contextual design modeling techniques, create a special part file containing the master surfaces of the aircraft (fuselage, wings, etc). I don't understand how this could be demonstrated during a job interview.