In order to get the Togepi Egg in Pokémon HeartGold, you will first receive an Egg from Mr. Pokémon that you will have to give to Professor Elm however Professor Elm will have 1 of his aides give you the Egg (which is the Togepi Egg) after you interact with him in the PokéMart in Violet City after beating Falkner, the Violet City Gym Leader.
For a togepi to evolve you need to give it 220 happiness
Continue with the game
Togepi
you get it from an egg in Pokemon platinum
he hatches
A Togepi.
I don't know if it is the same on heart gold as it is on soul silver, but the Pokemon that hatched for me was a togepi. Hope I helped!
For a togepi to evolve you need to give it 220 happiness
After going through a little bit of the game, Professor Elm contacts you telling you that a scientist of his is holding an egg that he would like you to carry with you. The scientist is in a Pokemon Center, and you can pick up the egg from there which will hatch into a Togepi.
The egg is what Pokemon lay when you breed them with males and females (or dittos with other Pokemon) they hatch when you run enough or ride on your bike enough and hatch into the female Pokemon not the male
a togepi.
Continue with the game
Togepi
you get it from an egg in Pokemon platinum
he hatches
You can only get Togepi in Pokemon Emerald by trading from another game. Togepi is a baby egg Pokemon that prior to Gen 4 was normal type Pokemon.
you need to hatch a togepi in soulsilver or heartgold then trade it to pokemon diamond