Whitney is in Goldenrod City. She has a very strong Miltank so have at least one Pokemon stronger than Level 25
in mohgaony town
Viridian city
It is in Mahogany town in the southwestern corner of the town.
Blackthorn City, after Mahogany Town and after Ice Path
you would have to go look for her she is out of town where bill's house is then you can battle her at the gym.
Cinawood city, which is in the next town after the one with the lighthouse.
you need the 2nd badge, from the bug gym leader, which is from the gym in azalea town.
blackhorn city i think its next to mahogany town
Go to the route south of the city faulkner is the gym leader of and then through union cave
yes it is in Azalea, but you have to save the slowpokewell before battle the gym leader
I'm guessing you have to defeat all 16 gym leader's before you attempt that...
Chuck, the fighting-type gym leader, is located in Cianwood City, south of Olivine City. You'll need Surf to reach the town, though.