Visit Shrine of the Flamebringer in Western Stillsnow Wilds, which is the area west of the town of Snowstill where Primrose’s second chapter is marked on the map. The shrine cave entrance is a little tricky to find in this large area - head southwest from save point and the path will take you through a rock arch then to the east. The cave is snow covered with a torch outside it. The mini map market for shrines looks like UUU so you can look for that as well. Enter and press A on the shrine and achievement pop.
I wouldn’t rush getting this or the other secondary job achievements as the areas have much harder battles compared to the starting areas for chapter 1. Be at or just a few levels below the “danger level” shown on screen when you enter areas.