"What book are you going to read?"
Translation:¿Qué libro vas a leer?
See territech. However, using "which" instead of "what" signifies that you are probably making a choice from a smaller number of books. Using "what" probably indicates that the number of books from which you can choose is a larger number. This is not a firm rule and you can swap the words without being wrong, but speaking as a native speaker, I would do it that way.
As I understand it, the "te" is used as a reflexive to indicate that you want it for yourself and not for somebody else, while the "tú" is the optional subject pronoun. Sometimes spanishdict.com gives the word-for-word meaning without taking into account how native speakers put together words to get meanings specific to their language.
The "va a + infinitive form" is translated as either "is going to + infinitive" or "will + verb." So " ¿Qué libro vas a leer?" can be translated either as "What book are you going to read" or "What book will you read." It is my understanding that native speakers prefer to translate "va a" as "is going to" because they think of the meaning as progressive. In English, conversely, we think of "is going to" as another way of thinking in the future tense. Either way, the words are the same, but the grammarians of each language categorize the tense differently.
Reflexive pronouns are used when translating English passive voice sentences (which contain a helping verb that is some form of "be" + a root verb, for example: is reading) because there is no literal Spanish equivalent to English passive voice.
What this means is that the "vos" doesn't need to be added to this sentence because the verb leer is not reflexive. Nowhere in the English sentence is there any indication that the subject of the sentence is reading the book only to himself and being affected by doing so. In fact, the subject of the sentence could be reading the book to someone else. The reflexive can be used when the action of the verb is going to affect the subject, but in this case, the subject of the sentence is not affected. The question is not about the reader but is about what book is going to be read. For the record, any time Spanish used any form of "ir" + a + infinitive, the usual translation is "is going to + root verb." An alternate translation is: will + root verb: What book will you read?