I have had him for two weeks its really hard for him to eat the pellets

He is Around 6-8 Inches
Feeding:Hikari Cichlid Staple Gold Pellets(Medium Size)

Its rare for him to get one in his mouth

He hasn't got locked jaw because i put a mirror in-front of the tank and he opens his mouth and jaw all the way

It is almost as if he's not opening his mouth wide enough. However, it seems that he can see the food. Have you tried slightly smaller pellets? Maybe try some sinking food and see how he gets on. Hopefully perseverance will prevail

I just got some small sinking pellets and he ate them

but i feed my other oscars in another the floating pellets and they eat them with no problem and they are an inch smaller

As long as he eats, a special diet won't hurt.
Then he'll just eat some more pallets.
Try handfeeding mealworms, that might work, if you want to feed some live food.
When I feed my O pallets, he looks at me as if to say: That's no food!
He's spoiled!

Oscars, under stress, can be difficult. The stress associated with a new tank, especially, can cause oscars to sulk, pout, or even go on hunger strikes. Once they adjust to their new environment and/or their new owner, they come around . . .