Don't want to write this by hand? GodCraft sets minecraft:managed_wandering_trader for you with a switch.Get GodCraftOverview
minecraft:managed_wandering_trader is an entity component: it goes in the components object of a custom mob, or in one of its component groups. Handles part of the wandering trader's built-in behavior. It is meant for the vanilla wandering trader and has no settings.
Example
Inside the components object of BP/entities/<name>.json (values are the defaults or placeholders):
BP/entities/<name>.json
{
"minecraft:managed_wandering_trader": {}
}