"Do you hear me?"
Translation:Bạn nghe thấy tôi không?
The simplest way to explain this is by using a few examples in English.
"You eat vegetables, don't you?"
"You do eat vegetables, don't you?"
In the second English sentence, "do" is used but is not strictly necessary. It might put a bit of emphasis on the verb that follows it -- "do" in this example -- but not required. "Có" could be thought of as doing the same function as "do" in the English sentence, but the emphasis is even less strong. Or it be thought of as just a matter of style.
The point to take away here is that "có" can be used in front of a verb as a mild emphasis or a matter of style without changing the meaning of the verb.
(Of course, by itself, "có" means "to have".)
"thấy" is not necessary, it only serves to confuse beginners. One can say, for examples,
"Bạn nghe tôi không?"
"Bạn có nghe tôi không?
"nghe" means "hear" and "thấy" means "see" ; together they are usually used in a generic sense, meaning "to be aware of", "to be familiar with", "to know of", "to have news of", etc. For examples,
"Bạn có nghe thấy gì về nó không?
(Have you heard from him? Have you got any news from/about him?)
" Đâu có nghe thấy gì đâu! "
(Have not heard anything!)
Hope this helps.