i go to mossdeep city
Go to Sootopolis.
sootopolis city
in the fortree city
You battle the 8th gym leader, Clair, at Blackthorn City.
Wallace he was the former 8th gym leader in ruby and sapphire
He is at Sootopolis city...you can battle him only after the sootopolis incident
In Sootopolis City.Trainers and Gym Leader uses Water-Type Pokemon.
Sunnyshore City
Go to Evergrande City to beat the Elite Four
The only way to get a gym badge is to challenge the corresponding gym leader and win.
Petalburg city he's in the gym and you battle him for your 8th badge.
It's in the gym when you're done defeating the leader he will give you the TM (8th badge)