data/trinkets/entities/sc-goodies.json

{
  "entities": [
    "player"
  ],
  "slots": [
    "hand/glove",
    "feet/shoes"
  ]
}

data/trinkets/tags/items/hand/glove.json

{
  "replace": false,
  "values": [
    "sc-goodies:item_magnet"
  ]
}

and the feet/shoes one is a pretty long one, so I won't post it.
but yeah, I can't place my trinket (sc-goodies:item_magnet in this case) into the hand/glove slot.

docs are wrong they're saying data/trinkets/tags/items, while it should be data/trinkets/tags/item