What programming language should I use on a Raspberry Pi 3 to implement a Graphical User Interface for a kiosk where people can get insurance quotes by providing info and uploading documents? Much help will be appreciated.

It's pretty easy to set up Node.js

use a node js platform to write your gui in js and html. you can find desktop node frameworks. its the easist solution for linux

Python is a favorite for RaspberryPi, and should have ui integration in there. With node, you'd probably end up building a web interface, but not a requirement when working with node. There are some libui bindings available for node

I think you can use Qt with C++ or Python to develop the UI

Is there a way to use a web interface but securely upload and store sensitive documents (driver license, etc.)?

@iKAANIK how would they upload stuff at a kiosk? from a pendrive?

@cantleave like a scan in or something. Im open to ideas

Python and Tkinter

@jirehstudios I agree! Tkinter is a great library for GUI. simple and easy to use.

I would go with the web interface. Doesn't matter if you use node, python, php... whatever... But I think it makes sense to make it a web interface