can you also say "you are from where?"
I've never seen that, formally speaking. Then, it will depend on the context (for example, if you want to confirm what someone has said).
"és de onde?" is correct when we refer to someone as "tu". Can we say also "De onde tu és?
Yes, both options are correct.
Ok, one more. Is also "De onde vens?" correct?
I saw equivalent for você : De onde você vem?;De onde você é?' Você é de onde? so I wonder if above version for "tu" is also correct.
Yes, it is also right.
I have heard it constructed that way to emphasize "where," often to suggest surprise or confusion on the part of the speaker.
"I am from Opa-locka"
"You're from where?!?!"
Technically you could, as a clarifying/follow up question....
"Hey, I'm from Cnriehdk"
"You are from where?"
But as for the natural purpose... no. It will always be... Where are you from?
In Spanish: De donde es usted?
De onde você é? is ok
This can be translated as "Whence are you?" It's formal, but it's correct.
Why were we previously taught to say "De onde você é" ?
Both options are correct.