Head West out of town on Route 16. Then you need a Bike (You got one from the guy in Goldenrod right?) to take 17 and onto 18 and over to Fuchisia City.
The Gym has a hidden wall maze with the added bonus of all the Trainers looking like the leader. (Spoiler the one you want is in the exact middle). Head immediately to the far right and walk straight up the entire length of the gym. Then cut left past the heart door to the far left wooden door and head down. Head right one slot and go down to the right of the faker Trainer and then walk left above the Trainer and then down and right until you get to the middle Trainer is actually Janine.
lvl 47 Crobat, lvl 44 Weezing, lvl 47 Ariados & lvl 50 Venomoth vs lvl 65 Typhlosion
Soul Badge - Badge Battle