Wandering Trader farming is the process of farming wandering traders for their trades, and/or disposing them and their Llamas to get Leads and Leathers. It's a farm to build to glitchlessly renewably farm items like Sand, Red Sand and Small Dripleaf. However, in a normal Minecraft world, all those things are easy to get, so it isn't the most practical farm. Additionally, it will require several Emeralds, so you might need to have a VillagerTrading Hall or Raid Farm. This farm is generally only useful for single Biome or other types of Survival Challenges, where some resource are limited (for example a Ice only world where you can't get Red Sand).
Concept[]
Wandering Traders spawn infrequently, so there wouldn't be an efficient way to get large amounts. Below is a general concept of what the farm can look like, keep in mind it hasn't been tested on a large scale:
There will need to be a platform over somewhere that can't spawn mobs, such as the Ocean. There will need to be a Bell in the middle, a hole around the Bell with Trapdoors to trick Wandering Traders into walking over it and a Water stream in that hole which will transport the trader to the player. There will also need to be a system which will activate and deactivate a Dispenser which will dispense Lava to the trader after the player is done trading (using a Lever is best), and also Signs and a collection system so that the Leads and Leathers won't be burnt.