You can use any programming language to make a quiz app. It mostly depends on what platform do you want to create it.
As far as sololearn is concerned. It just randomly pick up question from its database(questions submitted by community and developers) and gives it to you to solve
To make a data-centric web app from the bottom-up, it is advantageous to understand:
Backend language (e.g. Python, Ruby) - control how your web app works
DevOps (Github, Jenkins) - Deploying / hosting your web app