A JavaScript graph plotter for schoolchildren using paper.js
I'm not familiar with Paper so can't say anything about that. And I won't say much about the HTML, as it's obviously just a functional placeholder, except two points:

Use double quotes &quot; consistently on all attributes.
Don't use on... attributes. Assign event listeners in the script using addEventListener.

Regarding the script:

Use let/const instead of var.
Declare the variable in loops separately in the for statement using let (e.g. don't reuse the same declared variable in all loops).
Use better variable names. I have no idea what z, zz, node2, code2, etc. mean. (Also make sure all variable names start with a lower case letter.)
Don't repeatedly create the same colors in the loops. Create them once outside the loop.