Enter your seed. Every trial chamber appears on your real overworld terrain and the panel lists the nearest ones to the center of the map with distance, direction and exact coordinates.
The coordinates are the chamber's starting chunk; the chambers are underground, usually between Y=-40 and Y=-20.
Easy one: since 1.18 the same seed gives the same overworld on Java and Bedrock, and trial chambers are one of the few structures Bedrock places exactly like Java. Same map for both.
Java positions are built on cubiomes, a re-implementation of Minecraft's world generator, and I checked them against worlds made by real Java and Bedrock servers. If you find one that's off, tell me in the comments with your seed and coordinates and I'll look into it.
Reference: Trial Chamber Finder
Trial chambers arrived in 1.21 (Tricky Trials): underground copper and tuff complexes built around trial spawners and vaults, and the only source of the mace.
Getting the mace
The mace is crafted from a heavy core and a breeze rod. Heavy cores come from ominous vaults, which need ominous trial keys, which drop from ominous trial spawners. Drink an ominous bottle (from pillager captains) before entering a chamber to turn its spawners ominous.
Trial spawners and vaults
Trial spawners scale with the number of players nearby and drop trial keys when beaten. Each vault opens once per player with a trial key and gives armor trims, enchanted books, diamonds, emeralds and more.
Where they generate
Trial chambers are placed on a grid of 34 by 34 chunk regions and generate underground in nearly every biome, typically with their center between Y=-40 and Y=-20. Caves often cut into them, which is an easy way in.
How do I find trial chambers?
Enter your seed and every trial chamber appears on the map with exact coordinates; the nearest ones are listed with distance and direction. They are underground, usually between Y=-40 and Y=-20, so dig down at the coordinates.
What is in a trial chamber?
Trial spawners that summon waves of mobs (including breezes), vaults that open with trial keys, and ominous vaults with the heavy core used to craft the mace, plus the flow and bolt armor trims and wind charges.
How common are trial chambers?
Common: they are placed on a grid of 34 by 34 chunk regions and generate almost everywhere underground, so there is usually one within a few hundred blocks.
Does this work on Bedrock?
Yes. Bedrock puts trial chambers in exactly the same places as Java for the same seed, so the map works for both editions.