From a scientist.
4 all i know each Pokemon trainer games have only one Exp. Share in the whole game
you could switch Pokemon in battle then all Pokemon that battled get exp or you could get the exp share and give it to one of your Pokemon
use the exp share
Once you get 35 Pokemon in your PokeDex, Prof. Rowan's aid will give you the Exp. Share in Eterna City's gatehouse.
An exp share allows you to share exp with another Pokémon. You can get it in Pokémon Diamond Pearl and Platinum near Eterna City.
give the exp share to a weak Pokemon when you use any Pokemon to fight exp goes to the fighting Pokemon and the 1 with the exp share.
give the Pokemon you want to train an exp share then put your strong Pokemon first on your team and train on high leveled Pokemon the Pokemon with the exp share should level up by itself!
In diamond and pearl it is 35. an it is an EXP SHARE not and esp shard.
if you want strong Pokemon to beecome stronger, than give it the exp share while battling. it gives you double experience. if you want to raise weaker Pokemon, give the exp share to the weak Pokemon, then battle. in soulsilver, catch the red gyarados and where it was is where the red scale is. go to mr. Pokemon's house, and he will give you the exp share. in pearl diamond and platinum, you get it from............................ sorry, i forgot. Google search "where to find the exp share in (blah blah blah). hope this helped :D
an exp. share works on any pokemon your welcome
professor oak gives it to you
Players can obtain the exp share item in two ways in the Pokemon Pearl Game. One of Professor Rowan's assistants will give one to the player in the entrance building to Cycling Road if the player has recorded 30 or more Pokemon in the Pokedex. A player can obtain a second exp share if one of their Pokemon's ID numbers has the first three digits in common with the Pokemon Lottery in Jubilife City.