Trigger a Pillager raid by defeating one of the evil grey villager like guys with a flag above his head. He usually is in an outpost or wandering the world with two normal crossbow guys. Once this is triggered a raid starts, fend off the waves and you will get a a green icon 'hero of the people'. This lets you get a discount when trading.
Now book it to a nearby village and do a few trades with a villager to pop this trophy.