Two functions are called: void updateControl() and updateAudio().
The updateControl() can set the wave shaping and so on.
This is the explanation, http://sensorium.github.io/Mozzi/doc/html/group__core.html
But I find it hard to understand all the functions and how they are used.
If you take a look at the example "m_05_AMsynth.ino", it plays random notes. That is done in the UpdateControl() function.
You could use a potentionmeter to change things in the UpdateControl() function.
To get the value of a potentiometer, you could use analogRead().
This is an example how to use a potentionmeter as input, https://cs.marlboro.edu/courses/fall2012/gadgets/notes/MozziTest.ino_html
This is an example of a complete project with a potentionmeter used in UpdateControl(), http://www.cs4fn.org/arduinitar/
This is the most interesting, but I can't find the source code: