He is in Sandgem Town, in the Pokemon Lab after you see all the Sinnoh Region Pokemon. He will present you with the National Pokedex.
After your pokedex is complete (note: you do not need to own all the pokemon) visit Professor Rowan. Professor Oak will come and give you the National Pokedex. After, he's in Pal Park, which is at the end of route 211. You'll see him there, then he'll leave. After that, he's in the last house to the left in Eterna City.
you have to fight all the Pokemon trainers and then you go to proffeser oak and then you go on a boat to the survival area
you pick a squirtle from the Pokemon proffeser oak gives you to choose from
Show it to Proffeser oak
you need all of the national dex Pokemon then talk to proffeser oak
You have to go to this guy in Pokemon centre and he will ask a question and say no and he will give u a pokephone and then go to proffeser oak and your mum.
you get it when you see every single Pokemon in Diamond or Pearl, then go and speak to proffeser rownan
proffeser oak gives you rock climb in one of the citys in kanto
you get a master ball from proffeser rowen to catch Dialga
Professor Oak's aide is in the Pokemon is Gay ravine of the Viridian forest.
From proffeser Oak.
he gets him from proffeser oak
he is in entera city somewhere below the Pokemon center i think but i noe its in entera city