Wandering trader farming is the process of farming wandering traders for their trades, and/or disposing them and their llamas to get leads and leather. 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 villager trading hall or raid farm. This farm is generally only useful for single biomes or other types of survival challenges, where some resources 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 leather won't be burnt.