you go through the route where Valley Windworks is and go through the Eterna Woods and you will be in the city where the second gym is.
battle the trainers and proceed
The second gym is in Eterna City. The gym leader is Gardenia, who specializes in Grass-type Pokemon.
The fifth gym leader in Pokemon platinum is crasher wake but you get the fourth badge.
go to hearthome city
The water Pokemon gym leader is in Pastoria City.
where can i find the second gym in Pokemon platinum
Train it so it can have resistants
The Gym Leader of the Snowpoint Gym.
The eighth gym leader in Pokemon platinum is the one in sunny shore city.
You use your strong(est) Pokemon to kill the Gym Leader's Pokemon.
Do you mean a gym leader?
The forth gym leader is in Veilstone City
by beating the gym leader