At least in American English, the only one of these that is correct is "how are your studies." The other ones are either grammatically incorrect or not really consistent with the ways in which Americans use the language.
First of all, "how is your studies" does not work grammatically. The word "is" is used with singular nouns. But the word "studies" is a plural noun. So these do not agree with one another.
You could then say "how is your study" because "study" is a singluar noun. However, Americans do not refer to a person's study (except perhaps as a room -- you might have a room called a study). If you are talking about such a room, this is okay, but in terms of what you do in school, we do not talk about your study.