Mineshaft Finder
Edition
Version
Seed
Mostly underground, between the surface and the deep caves. In badlands they can generate higher up, out in the open, built from dark oak.
Any chunk can start a mineshaft, so there are a great many of them. Zoom in and they appear.
On Java Edition, type /seed in chat (it needs cheats on, or operator rights on a server). On Bedrock, open the world's settings: the seed is listed under Game.