you can check (and define) which model is used for which mob inside their client entity files (the entity folder in the pack's root). in the vanilla resources; zombie villagers, evokers, and vindicators use geometry.[entity_name].v1.8, stored in models/entity/[entity_name].geo.json. note that by "entity_name", i do not mean the entities' internal IDs (the evoker's ID is "evocation_illager", which is only relevant for the entity file).
wandering traders use the same model as regular villagers for some reason, which is geometry.villager_v2, stored in models/entity/villager_v2.geo.json.