every time i ask him a question he just repeats it right back to me.. like "do you want some water?" he says "want some water?" (i usually take this as "yes").
"did you hit your sister?" he answers "you hit sister?" (not sure what this means sometimes when his 6 month old sister cries he says he has hit her but he really hasn't???)

i've seen other 3 year olds even 2 year olds with much less vocabulary than my son being able to give a good "yes" / "no" answer to most questions so i am wondering if this is a form of language development issue.

he seems to grasp the idea of some questions that involve the word "what" or "which" for eg. "what did you do today?"
he usually says the same thing however like "i played with my toys" (no variation even if today he has gone swimming or done something else)

otherwise he has a good vocabulary range, can make sentences and sings songs,etc.

i don't know if this is related but he doesn't pronounce the "k" / "s" / "f" sounds properly. he says "pish" (fish),
"tik" (six) and "tar" (car).

i've had his hearing checked and this is fine.
please has anyone come across another child that does this? any advice would be greatly appreciated.

That is quite normal.
I would encourage him to say yes or no, if he repeats what you said just say to him yes or no, even if you know what he means get him to say yes or no, encourage him to say it and don't take repeating as an answer. my 3yr old DS is like that but he has moderate speech delay

If you think its not normal or you want some input, book him in to get a speech assesment. Not sure if its the same Au wide but its free in Vic for Speech(public). My son had an assesment and they suggested hearing loss and to get him tested. they were right and i was very thankfull for that. although it dosn't sound like that is the problem.

there are many condition that involves speech and the earlier you both learns to change/manage it the better. but hopfuly its just a leaning stage for him.

good luck

i think the pronounciation is fine but the question thing is funny

maybe try some really obvious role playing with your partner ie Do you want a drink of water" "yes please" and you give him a glass of water.

and try delaying giving your son something until he answers with a yes

i dont know though just suggestions.

my DD1 has been answering with yes and no since 18 months and gave nodd yes answers much earlier than that i think.

My DS (almost 3) has a question problem too, but instead he asks questions instead of stating wants/needs. Eg, he will say "do I want a glass of milk?" rather than "I want a glass of milk".

He also has the same pronounciation issues as your DS.

However he has been speaking in complete sentences for more than a year, has an outstanding vocab and demonstrates an understanding of abstract concepts, so I'm not worried.

I think they're just experimenting with patterns of speech and language rules. English is a very complicated language; even for native speakers it takes a fair while to get the hang of it (some people haven't even got it right as adults).

I wouldn't worry if I were you.

I think that you should have him assessed. This type of repeating questions back can sometimes be a sign of autism. I certainly don't say that to worry you but I think you should see a specialist just to be sure everything is okay.