So khi nào can be used at both the start and end of a sentence?
Could it be ''when do you read books'' or would I need a plural marker for that?
No, it couldn't.
"When do you read books?" could be "Khi nào bạn đọc các/những cuốn/quyển sách?" or simply "Khi nào bạn đọc sách".
Do I choose one of các/những AND one of cuốn/quyển ?
You can choose one from each pair. They all are accepted.
Is it having 'Khi nào' at the beggining of the sentence the same as having it at the end like in 'Bạn học tiếng Việt khi nào?'? Thanks
Yes. Khi nào can Be used at the beginning or the end of the Question .
Khi nào bạn đọc quyển sách = when do you read the book?
Bạn đọc quyển sách khi nao = When DID you read the book?
Quyển/cuốn sách gives me the nerve every time. Personally I find it very difficult to hear the difference in pronunciation.