JSON is the way to go, its simple nature makes it fitting for writing dialogues. It's the fundamental structure of Twine and other new dialogue system.
There's not much tutorial available, but I can assure you that it's easy to learn, just read the JSON documentation. construct.net/en/make-games/manuals/construct-3/plugin-reference/json
Play around with it and you'll get it quick.
If you have money to spare, you can buy this dialogue system I've found, it supports Construct 3 with c3runtime, according to the description. scirra.com/store/royalty-free-game-templates/dialogue-system-template-699
This should help you make a dialogue system using JSON.
For the dialogue generator, similar to Twine, I've found this tool, if you have another spare cash, you can use this: radmatt.itch.io/dialogue-designer
It exports the dialogue you've created from the editor, into JSON. Which you can use the built-in JSON plugin to parse the data.
Or, you can still use Twine and parse it manually using the built-in JSON plugin too.
I hope that helped.