what was it that you really wanted? or what is it that you really want?
但是 what do you really want? 这句话是不错的。但是貌似强调你到底想要什么。 what really do you want貌似也可以,就是强调(你要的)到底是什么?不过听起来有兄大早点怪。一般会说 what really do you want to do/see/get....
如果两句选,后面一句一定是没错的。 至于羡雀”what you really want"是口语化的,写出来不要这么用,除非是quote别人的对话。