How to write a bot for minecraft?

Question

Java

1. In which file is the player's nickname stored?
2. What exactly to interact with? (I don't think you need to open the minecraft jar)
3. How to get the pressed key?

Answer 1

1. In which file is the player's nickname stored?

Look somewhere in the launcher configs (I won’t tell you a specific place. Depends on the launcher)

2. What exactly to interact with? (I don't think you need to open minecraft jar)

If you are making a bot for a network game, then you will need to interact with the API through its protocol.
Here you can find its description:
https://wiki.vg/Protocol
If for a single player, then you will either have to interact with the game's GUI, or make a mod that will call some internal functions.

3. How to get the pressed key?

google: "Get pressed keyboard key Java"