Resolved questions
Are correct to say "You have?" or only "Do you have?"? - How to use "do" ?

You have [a light]?

This is an example of "ellipsis". There are a number of rules to observe when talking this way. You will have to study them by yourself. Any good grammar book will teach you this stuff. You can Google it too.

There are four main types of questions in English object questions, subject questions, indirect questions and tag questions.
Most questions are object questions. To form object questions we normally invert the subject and the verb ( for sentences with 'to be' or modal verbs) or the subject with the auxiliary verb for nearly all other verbs in English. Most verb tenses already have an auxiliary verb in the affirmative structure so we don't need to add one. Have you been to New York? Are you working tomorrow? 'Will you marry him, if he asks you? etc etc
The present and past simple do not have an auxiliary verb in the affirmative form so we add do/does for the present and did for the past.
Do you have a dog? Did you go out last night?
It is not correct English to start an object question with the subject even though some people may do this.
With 'have' it is possible to ask 'have you ?' but this is an abbreviation of 'have you got?'

We don't invert the subject for a) subject questions because the question word is the subject.
'Who wrote War and Peace?'
b) Tag questions because the inversion happens in the tag. 'You have three children, don't you?'
c) In indirect questions 'She asked if she could have an ice-cream.' 'He wanted to know what time it is.' (NOT what time is it)
So if you want to speak correct English you have to remember the do/does in present simple object questions and the 'did' in past simple object questions.
Use this to help you remember..
QASI = Question Auxiliary Subject Infinitive
ASI = Auxiliary Subject Infinitive

Please, use "do you have..?"

Cutting out the "do" sounds like you cannot (or are too lazy to) speak English properly. Even when you can get away with using "You have...?", it's a very direct question and can sound rude.