You need cut, or the ability to go through diglets cave, then he is in a route separator building
Chat with our AI personalities
He is east of Fuchsia City, in the gaurd house separating route 15 from the city. Go up the stairs, and you will find his aide.
He is somewhere to the right you need Cut to get to him.
Professor Oak cannot be seen on Route 2.
Route 225 is not a route that can be found in Pokemon Firered, route 225 is in Pokemon Diamond, Pearl, and Platinum. To get there is Diamond Pearl and Platinum, you have to see every Pokemon in Sinnoh, then talk to Prof. Rowan and get the national dex.
In the big building either it's west of celadon city or fuchsia city but there is a prof oak aide inside on the top floor and he gives you the amulet coin if you have registered 40 Pokemon in the pokedex.