Answer 1

The EVs will be wasted. Shedinja always has 1 HP, it will never gain any points from EVs in HP.

The only viable EV set for Shedinja is 252 Attack, 252 Speed.

Comments

To expand on that, a Shedinja's EV training should really only focus on Atk, Spec Atk, and Speed. Use the EV-reducing berries on Shedinja to eliminate all those HP, Def, and Spec Def EVs so you have more room for useful EVs.

Answer 2

Nothing shedinja is set with 1 hp it cant get anymore. thats like the only downfall with its ability. but you can use it one attack, speed, and sp. attack.