To build up trust with your Pokemon you should:
-Put it in your party and walk with it
-Give it stat boosting items
-Have it battle
or
-Level it up
Chat with our AI personalities
Get the national pokedex and go to the Great Marsh. trust me i got this info from Bulbapedia.
how to get a togepi in Pokemon platinum
There is no grunt that you can give a Pokemon to in Pokemon platinum.
That pokemon is Azumarill in pokemon platinum in the national pokedex
No, you cannot get Jirachi in Pokemon platinum.