It's often unnecessary, however, it's not incorrect.
A possible conversation:
Person 1: We're going to there.
Person 2: To where?
In the above example, person 2 reaponding with "where to?" would be strange. It would imply that they didn't hear person 1's statement.
Either way, it's not incorrect to say "To where" even if the usage is uncommon.
Does it mean that ""Papai, onde você vai?" is wrong, and it should be ""Papai, aonde você vai?" It is in Duolingo, so I wonder if it is wrong or both adverbs could be used: https://www.duolingo.com/comment/2286504. There was also phrase "De onde vós vindes?" , this is also about movement.
deveria ser "Papai, aonde você vai ?" e "De onde vós vindes?", está ok, visto que deseja-se saber "de onde", "de qual lugar".
I really wish the content editors could develop some consistency concerning literal versus "natural" translations. Half the time I go for the literal translation, I find the only accepted translation is adapted to fit common English linguistic styles. And half the time that I go for a more "natural" translation, the only accepted answer is completely literal even though virtually no one would ever construct such a phrase in English. I am finding that I'd rather pay for a program that isn't so arbitrary. I really don't like to be negative, especially since this site is free to use. However, I am finding that it's frustrating me more than it's serving to reinforce the Portuguese I have already learned.
I have tried many courses, paid and free, and let me tell you that none have worked as good as this one with the exception of "Living Language" which is very good, but hey if I have to choose between carrying around books and having the need of a CD player or use my phone which I carry around always and includes writing, speaking and pronunciation... I think the choice is clear. (And I haven't yet mentioned free vs. paid) So what if you make a mistake first? It'll correct you and for the next time you can make it right, plus I love losing all 3 hearts! It helps me get more practice.
I've only been on here a month and that was my initial experience but there was so much positive energy going on I persevered and I'm glad I did. Report any answers you find that do not sound natural. This is a learning algorithm and from what I have seen it is learning fast and learning well. I'm now finding that answering with a very literal translation that makes little sense in English is more likely to lose me a heart than answering in a natural manner. And, hey, these hearts are free. Practice is good. I used to beat my head on the table when I lost one. Now I just think: hey, another free chance to practice. When I make it fun I learn more.
My confusion is often caused by that strange 'fog' - it seems to me anyway - that Romance languages call the 'subjunctive'. In the example here 'Aonde ele vai?' there must be uncertainty on the part of the questioner, so why not say 'Aonde ele vá'? Do you draw a distinction between uncertainty and doubt?
Oh, yeah, it's damn complicated indeed. But in this case, even if you don't know where he's going, you're certain he's going somewhere, so you're not expressing doubt. You would be expressing doubt by saying "não creio que ele vá" (I don't believe he's going / he'll go).
It's hard to explain since for a native speaker these things are usually second nature, but maybe this link is helpful: https://www.duolingo.com/comment/9508268
Well, as doubt seems inextricably linked to uncertainty, I would have thought you were expressing your doubt by the open-ended question as much or more than someone answering 'Talvez ele vá para casa' or 'É improvável que ele vá para casa', where the subjunctive is triggered AFAIK, although these suggestions refer to only one possible destination. Thank you for reminding me of this link though, which does set out the uses of the subjunctive clearly.