As @okyeron has stressed, Norns does not run PD.
The norns documentation goes into more detail about the platform; the section on maiden walks through how the in-built visual package manager works, and the studies will introduce the coding environment. Broadly, the underlying technologies are SuperCollider for DSP, and Lua for building interfaces and interactions. This sits on top of core C-based infrastructure and other moving parts, like the web-based editor.
It is not necessary to write both Lua and SuperCollider; the majority of people writing Norns scripts are writing Lua, and integrating either with existing SuperCollider “engines”, or with the built-in audio buffer manipulator softcut.
The docs are pretty good, though, as a starting point to clarify some of this.
