Head to Phonm Nonh in the Southern Champs Sauvage region and look to the left of the Inn to discover an old man with a request. He wants a material from the Brollygaggers outside to make a lamp.
Head outside of town and if it's not raining, head to the nearby Camp and continue to rest overnight until it is. Once the rain starts pouring, look for the Brollygaggers in the surrounding area. Simply defeat one to get the material and return it to the man to complete the request.