how to represent a function for which the exact form is not known?

Questions
1

Suppose, ?, y and z are three basic independent variables.

x is a variable which is a linear function of ?.

p is another variable which is a function of ? and z, but not y, and the expression of p in terms of ? and z is not known.

  1. How to write them in sequence?

  2. What will be the results of D[p, ?], D[p, y] and D[p, z]?

2

What about

x = a*\[Theta]
p = pf[\[Theta], z]
D[p, \[Theta]]
D[p, y]
D[p, z]