If you mean the man that says he had a dream that someone would bring him a Remoraid, then he's by the sea on the road to go to Sunyshore City in one of the little houses by the guy who has lots of Pikachus.
route 221 from the old man (like the newspaper) you must bring him the Pokemon he wants and there is a new one every day
fisher man
in eterna city
At the museum in Oreburgh City there is a man that will get the pokemon out of the fossil.
The shay man is on Route 225.
a fisher man on route 222 has it
Go To Floroma Town You Should See A Entrance On The Corner Of The Town You See A Man, And That's Where You Get Honey In Pokemon Platinum.
He is in Eterna city next to Pokemon center!
yo man you cant
no man gives you a happiny platinum only in diamond and Pearl
talk to the man in the Pokemon fan club building in hearthome city.
In Pokemon Diamond and Pearl you will have to go to route 228 and talk to an old man, I think you might have to do the same in Platinum.