You go up from Cherrygrove there will be a house DONT go in it keep going up to the next house if im wrong dont get angry I did it along time ago. If it was'nt the house I told you go in the 1st house in stead hope this helped :)
ProfessorElm tells you it's past Cherrygrove city. You go past the next house where the man says "how can you be so oblivious to my eye-catching house?!". He then gives you an apricorn box. You go past the tree next to his house and press 'A' once you've walked up to it and you shake it. Then go further north and you might want to have a repel (unless you can't get them yet) and go past the bug catcher and off to the left through all the grass where you'll find his house.
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Go a little past Cherrygrove and you will see a house with a red roof. That is not Mr. Pokemon, but the house of "The Apricorn Guy", as I like to call him. He will give you an apricorn basket which you can use to collect apricorns. After talking to him, go north (Up) a bit and you will see a different house by a ledge. That is Mr. Pokemon's house.
In Heartgold and Soulsilver, the House of Memories is in Lavender Town, which is in Kanto, East of Saffron City.
You need to breed Mr. Mime while it holds the Odd Incense
If you mean an Exp. Share then you go to mr. Pokemon's house at Rt. with the red scale you should have picked up after battling gyrados. He will take it in return for an Exp. Share
In a house that's in Ecruteak City.