I know ash's pika hates being in the pokeball but what did ash do with the pokeball that Oak gave him for Pikachu? does he still have it? and where does he keep it?

I'd've thought Ash would've kept the ball, just in case. As for where he keeps it.. his backpack?

He probably would've just thrown it away. No use for it. :/

And if he did keep it, "just in case", there've been a LOT of cases where he should've used it. First movie? Third movie? Eighth movie? Random episodes?

He tried to use it the first time he fought Brock, but it didnt work because Onix was Binding Pikachu and blocking it. I dont think its been seen since.

He probably has it in his backpack, or gave it to Oak at some point.

Um, doesn't he still have it in the first movie? He thinks Pikachu and the other Pokemon would be safe from Mewtwo inside their Pokeballs, but only gets to recall Squirtle and Bulbasaur, and then Mewtwo's Pokeballs catch the Pokemon from inside of their Pokeballs anyway?

Ash still does have Pikachu's Pokeball in at least one "random episode" that I can remember - that would be "Snow Way Out." He returns Bulbasaur, Charmander and Squirtle to their Pokeballs and is going to do the same to Pikachu until Pikachu practically clings onto him and begs to stay out to help keep Ash warm.

I would say he still has it. Possession of Pokeballs in the anime seems to represent ownership. This is why Ash and the Gentleman on the St. Anne wasted valuable time using the trading machine while the ship was sinking, or why Professor Oak and Tracey made a big deal about transferring Aipom's Pokeball to Ash when he arrived in Sinnoh.

yeah but in that episode Snow Way Out. he keeps telling Pikachu to get in the ball but hes not holding the ball we never even see it so even if Pika got in where is it?

nice question. he probably just has it somewhere in his pack so no random person finds it and returns pikachu, like Team Rocket