How can I read chat on a minecraft server using RCON?
You can't.
RCON does not support a scrolling (streaming) console, it only supports incoming traffic and one response, like a REST protocol. You could try ssh-ing or mstsc-ing (Microsoft Remote Desktop (lit: Terminal Services)) into your server with your server running in a container (for example, on Linux, this is in a screen (external tutorial)).
You can't do this in minecraft-java-edition, nor can you do it in any Source game such as counter-strike-global-offensive, team-fortress-2 or dota-2, where the protocol originated from.