Personally, I don't see anything wrong with asking people where they're from, unless you're planning on discriminating based on the answer. Also, I don't think you're supposed to ask this in job interviews in the US.
There are some sensitive Asian Americans that would take offense at this question because they perceive it as implying they're not real Americans. It's an identity crisis that many Asian Americans face, especially the young ones. My cousin, who's Taiwanese American, told me that she feels annoyed whenever someone asks her where she's originally from.
It also depends on who is asking the question. I hang out with a lot of Asian Americans and in the beginning people will ask each other where they're from. I'm always curious because as a Taiwanese I feel I would have more in common with someone whose family is also from Taiwan. Some people will even come right out and ask what kind of Asian you are and it's fine because it's coming from another Asian. But if a white person asks what kind of Asian you are it would sound racist.