When you beat Cynthia, go south of there and a enter the house. He is in there.
Prof. Oak is in a house in Eterana City.
in eterna city the house at the bottom of the city on the west.
after beating the game, go to pal park and talk to prof. oak. He will leave then you can find him in the empty house in eterna city and will tell you about sightings of MOLTRES, articuno and zapdos. you can track them with you poketch app.
Right after you get the National Dex in Sandgem Town. After that he is Eterna City in the southern most house before you leave the city, on the left.
After you get the National Dex, talk to Prof. Oak in a house at Eterna City. He will give you the Up-Grade to evolve Porygon to Porygon2 through a trade.
After getting the national pokedex, prof. oak will be at eterna city telling you that he spotted a moltres within sinnoh. It will be roaming around sinnoh just like latios in hoenn. It will be level 60.
in eterna city
Prof Birch is NOT in Diamond Prof OAK is in Eterna City.
Prof. Oak is in a house in Eterana City.
after getting the national dex you be able to find him in pal park then he will go off to Eterna city to the empty house that's to the left hand side of the Eterna city gym.
Bottom left.
in eterna city the house at the bottom of the city on the west.
By Prof. Oak in Eterna City after visiting him at Pal Park.
After you obtain the National Pokédex and visited the Pal Park, Professor Oak appears in the southernmost house in Eterna City.
Prof. Oak in a house in Eterna City.
He is at the bottom left corner in a house near victory road.
In the south, on the left hand side of the road.