Learn English – Tell me how you are? Tell me how are you

Yes and no: it is meaningful, but you have to interpret it in a very specific way.

The context is about the difference between
-something you know (for example, a password)
-something you have (for example, a key)
-something you are (that is, you yourself!)

The article starts by mentioning how we deal with how you prove something you know or something you have. "How you do you" is being used as a kind of shorthand for "how you prove something that you are."

It would be much clearer if it were punctuated differently, like

We decided to ask how you do "you".

because when they say "you" they really mean "perform the action of proving that you are who you say you are."

It really makes no difference to the meaning of the question which of the two you use, in today's common usage. Using 'which' sounds slightly more proper to me. I imagine that if the Queen of England were asking the question, that's how she would ask it. Needless to say, most of us don't speak like the Queen.

If you want to sound more natural you would probably say

Which floor are you on?

or

What floor are you on?

The prepositions are at the ends of these two sentences, which we are often told is incorrect. Still, most English speakers will say it that way in casual conversation.