Help understanding simple voltage regulator output
Yes, the Zener breaks down because of the 10V offset. The sine wave is to allow you to measure the impedance of the Zener model at the test current. 
From the datasheet you can usually find information that will help. Zx (dynamic impedance), for example, but it has to be specified at or near the operating current.  This particular type of Zener from Rohm is rather poorly specified- perhaps the model parameters were extracted from actual measurements, or perhaps they're not all that realistic.