Your ex-employer will receive notification of the hearing. They won't be "called" to testify. If they do not show up, the administrative law judge will take your testimony and will make a decision on your eligibility based on the information you provide and the relevant UC laws.
It appears to be a fairly straightforward issue which is whether the paycut and demotion were significantly different than your prior level of compensation and position to constitute "good cause" to resign. Generally speaking, there will have to be quite a significant difference. UC reg's frown upon someone resigning when work is available.
FYI - the ALJ will NOT rule on whether you were "wrongfully" demoted or whether the employer in any way acted illegal. That is not the UC Division's pervue. If benefits are granted, that does not imply that the employer did anything wrong or illegal.
A person, who is nice to you, but rude to a waiter, is not a nice person. (This is very important. Pay attention. It never fails.)