you got to the top of the sunnyshore light house and talk to the blond guy he is the gym leader then you can face him.
Go to the lighthouse and the Gym leader should be there.
In Sunnyshore City.
by doing everything else
in sunnyshore
That'd be Volkner who remains the Gym Leader there.
If your in sunnyshore city then just go to the gym and battle him.
his is in the lighthouse in sunnyshore city
go to sunnyshore city
go to sunnyshore city
Sunnyshore City
sunnyshore city if you have palkia
catch dialga the go to sunnyshore