Whitney ,she's at Goldenrod City.(Normal-type)After you defeat her she'll start crying.Talk to the nearest player and then talk to her and you'll get your badge.
Brock.
in blackthorn city
He is the Gym Leader in Cinawood.
you have to beat the last gym leader
you beat the last gym leader in johnto
You CAN NOT become a Gym Leader in Pokemon HeartGold and SoulSilver or ANY MAIN SERIES POKEMON GAME.
Not enough info: which gym leader?
In the goldenrod gym.
beat gym leader
Brock.
defeat gym leader.
in seafoam island
Jeff Gordon
in blackthorn city
He is the Gym Leader in Cinawood.
Simply beat the gym leader in every gym.
The eighth gym leader still awaits, as well as the whole of Kanto.