minecraft-assets/assets/minecraft/advancements/adventure/trade.json

{
    "display": {
        "icon": {
            "item": "minecraft:emerald"
        },
        "title": "What a Deal!",
        "description": "Successfully trade with a Villager"
    },
    "parent": "adventure/root",
    "criteria": {
        "traded": {
            "trigger": "minecraft:villager_trade"
        }
    }
}