Beat Volkner of the Sunnyshore city gym.
You can't you just have to beat him and get it
well put rock in lava, but on the place where you have 2 rocks put the uper one
Hearthome's badge
you get the coal badge after defeating Roark in eterna city
if you are looking for the third gym badge i suggest Veilstone city.
in the 1st gym badge
Beat the gym
you must beat the eighth gym leader and he will give you the badge.
Once you obtain a badge it's permanently stored in the badge case.
Beat the gym leader.
Get the first gym badge
If you have the Rakiou Member Pass (AR Cheat Code), go to go to the city where you got your first gym badge. From there go to the biggest building and talk to the lady at the counter.