I'm struggling to find where I should put custom advancements and if they need to be registered or something to show up in game.

Here's an advancement root I have in my resources/data/bountiful_boons/advancements/zeus. Of course, when I get a crafting table ingame it doesn't show.

 

{
  "display": {
    "icon": {
      "item": "minecraft:sapling"
    },
    "title": "Root",
    "description": "The root of this tree.",
    "background": "minecraft:textures/gui/advancements/backgrounds/stone.png",
    "hidden": false
  },
  "criteria": {
    "craft_table_pls": {
      "trigger": "minecraft:inventory_changed",
      "conditions": {
        "items": [{
          "item": "minecraft:crafting_table"
        }]
      }
    }
  },
  "requirements": [
    [
      "craft_table_pls"
    ]
  ]
}

 

Hmm, that all looks fine, I'm not sure why it's not showing up for you. Are you getting any loading errors for the advancement in your debug log or console output?

Also, FYI, the "requirements" item is optional; if all your criteria are required, you can just leave it off.

3 hours ago, arcticio said:

resources/data/bountiful_boons/advancements/zeus.

Is it named .json?

Sorry for the late reply, as far as I can tell there are no errors on starting Minecraft or loading in a world. Though, when creating a new world, I do get these warnings.

[20:31:53] [Server thread/DEBUG] [ne.mi.fm.co.ConfigFileTypeHandler/CONFIG]: Built TOML config for .\saves\E\serverconfig\forge-server.toml
[20:31:53] [Server thread/DEBUG] [ne.mi.fm.co.ConfigFileTypeHandler/CONFIG]: Loaded TOML config file .\saves\E\serverconfig\forge-server.toml
[20:31:53] [Server thread/DEBUG] [ne.mi.fm.co.ConfigFileTypeHandler/CONFIG]: Watching TOML config file .\saves\E\serverconfig\forge-server.toml for changes
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Configuration file .\saves\E\serverconfig\forge-server.toml is not correct. Correcting
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server was corrected from null to its default, SimpleCommentedConfig:{}. 
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.removeErroringEntities was corrected from null to its default, false. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.removeErroringEntities does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.removeErroringTileEntities was corrected from null to its default, false. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.removeErroringTileEntities does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.fullBoundingBoxLadders was corrected from null to its default, false. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.fullBoundingBoxLadders does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.zombieBaseSummonChance was corrected from null to its default, 0.1. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.zombieBaseSummonChance does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.zombieBabyChance was corrected from null to its default, 0.05. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.zombieBabyChance does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.logCascadingWorldGeneration was corrected from null to its default, true. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.logCascadingWorldGeneration does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.fixVanillaCascading was corrected from null to its default, false. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.fixVanillaCascading does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.dimensionUnloadQueueDelay was corrected from null to its default, 0. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.dimensionUnloadQueueDelay does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.treatEmptyTagsAsAir was corrected from null to its default, false. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.treatEmptyTagsAsAir does not match the spec. This may create a backup.
[20:31:53] [Server thread/WARN] [ne.mi.co.ForgeConfigSpec/CORE]: Incorrect key server.fixAdvancementLoading was corrected from null to its default, true. 
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server.fixAdvancementLoading does not match the spec. This may create a backup.
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfigSpec/CORE]: The comment on key server does not match the spec. This may create a backup.
[20:31:53] [Server thread/DEBUG] [ne.mi.co.ForgeConfig/FORGEMOD]: Loaded forge config file forge-server.toml
[20:31:54] [Server thread/INFO] [minecraft/MinecraftServer]: Preparing start region for dimension minecraft:overworld
 

The full path for the file is 

D:\Minecraft Mod\Bountiful Boons\src\main\resources\data\bountiful_boons\advancements\zeus\zeus.json