You need to have seven badges and you need to beat Cyrus and face Giratina in the Torn World. To find out how to do that, look on www.psypokes.com and go on the Pokemon platinum walkthrough.
in eterna city
He is in Eterna city next to Pokemon center!
To get the explorer kit in platinum you have to talk to the old man in Eterna City in the house next to the PC.
In veilston city behind the Pokemon center in that house that man gives you a porygon
you can go to a building in eterna city that has a man that will re name your pokemon. he is in a building near the biking route,but not the closest one.
there will be a man fishing in sunnyshore city
he means a serious NATURE
in eterna city
You must have the first 7 gym badges before you can continue ahead to Sunnyshore. Also I beat Cyrus and caught Giratina [platinum version].
At the museum in Oreburgh City there is a man that will get the pokemon out of the fossil.
sunnyshore city there is a poketch app man get 2 him with rock climb and do as he asks bring him Pokemon with different natures
He is in Eterna city next to Pokemon center!
NEXT TO THE MARKET MAN IN pastoria city
to get to sunnyshore city you have to do the dialga/palkia event on mt.coronet. after that you will see the man in the way is gone and you can walk there after a few trainer battles.
talk to the man in the Pokemon fan club building in hearthome city.
you beat the gym leaders and elite 4/cynthia you need the enigma stone which you get from a man in sunnyshore city then go to the spear pillar and it should appear
To get to Sunyshore City you must fight Dialga on Mt.Coronet, the the man saying there was a power outage will vanish and you can travel to the city.