• Data model
• Data-flow diagram
• Spike test
• Concept description and API explanation

Feedback:

Data-flow diagram
Data-flow diagram looks good and is clear. A minor thing I would specify more is 'other socket events'. What are these socket events and what do they do?

Data model
Data model looks good and is clear. A minor thing you can do is to make the data model more tailor made for your use case.

I can see quite a few functions that can be modulated in your server.js.
This makes your server.js a lot cleaner and easier to read.

You could add checkRoomCount(), sendUsers(), fetchNewPokemon(), modulateData() and sendPokemon() in a folder named for instance "helpers".

You can do the same for socket.io, just load it in from a seperate file, so that not everything is cluttered on one page.

While using the application, it might be nice for the users to see how much time they have left to answer

Since Express 4.16, bodyParser is no longer needed because it is automatically within the express package.
Therefore you can uninstall bodyParser and change it to express.json() or/and express.urlencoded({ extended: true }))

see: https://medium.com/@mmajdanski/express-body-parser-and-why-may-not-need-it-335803cd048c

Repo

• Missing a description and live link in the about section
• No env. or node modules, git ignore added.
• Concept, install notes, Data lifecycle diagram and external api added.
• Real time events section missing

Concept

• I understand your concept, It's a fun concept and I'm excited to see the finished result.
• Multi user functionality works as expected

Data life cycle

• Great data life cycle.
• Maybe you could name the "other socket events"?

Real-time Events

• You could refactor some of your app.js so that socket is loaded in from a separate file.

API

• It's clear what data the api offers.
• It's clear how to connect to the api, no key is needed.