I often hear people (mostly English learners) asking "How to ... ?" I think it is incorrect. But has this form of questions been accepted in contemporary spoken English?
An example:
A: "Can I have your name, sir?"
B: "My name is John Schwarzkopf."
A: "How to spell your last name?"
B: "S-C-H-......"
How to spell your last name?
I haven't heard it said that way. (AmE)
I would say:
How do you spell your last name?
or if you want to be more polite:
Could you tell me how to spell your last name?
which uses your example in part. Maybe someone shortened it somehow.
We categorically cannot ask a question using "How to?". It is bad English.
However, given the way we use search engines, we often find ourselves writing "How to cook a chicken" since we know that a tutorial telling us how to do so will likely have that title. This may have given rise to some learners of English thinking this is the right way to ask such a question. It is not. ("How do I cook a chicken?" or similar, is correct.)
As such, your example question is correct to use an auxiliary and subject.
How do you spell your last name?
How do you like your chicken?
