Irregardless of whether or not helen would or wouldn't use you all like a Southerner would or not, the first means what places did you (whether you is singular or plural is irregardless its own se'f) go. The emphasis is on the list of places the questionee went and the assumption is that there was more than one place. The second means where did the entire mass of you (in this case you is explicitly plural) go. There is no assumption of any more than one place having been gone to but it *is assumed that more than one person went and that they all went as a group.