Cosa means "what", "Che" can mean both "what" and "which" and "Qual" means "which".
For example: "Che cosa prende?" (is the correct form, whereas only "Cosa prende?" would be the abbreviated, colloquial form. "Che lavoro fa?" is also possible, instead of "Qual lavoro fa?".
«Qual» does not mean "what;" it just translates to "what" in this context. English just happens to not use "which" in these contexts, unlike so many other languages. Think of it this way: the total can be any number in a set of numbers. The person asking is just trying to figure out which, out of all the possibilities, the total actually is. It can only be so many things; it's not completely open-ended.
According to A Reference Grammar of Modern Italian (2nd ed), by Maiden & Rogustelli (2013),
"Quale?" is a pronoun or adjective used to request identification: possible replies to it would contain a name, a demonstrative (questo, quello), or even just the act of pointing to the relevant entity. It corresponds not only to English ‘which?’ or ‘which one?’ but also, sometimes, to ‘what?’
In contrast, "che?", and the pronouns "che?" or "che cosa?" request not necessarily identification (although they have this function, too) but definition or explanation.
The appropriate answer to "Qual è la capitale della Polonia?" [What is the capital of Poland?] would be "Varsavia", [Warsaw].
But the answer to "Che cos'è la capitale della Polonia?" [What is the capital of Poland?] one might equally reply, "È uno dei più importanti centri commerciali dell'Europa orientale" [It's one of the major commercial centres of eastern Europe]."
I speak french and what bothers me is the "il" why is the point of it .. the " qual è il tuo totale" in french becomes quel est ton total" . It would be so much easier if we could just say "qual e tuo totale". What is lost here ? Is it just a peculiarity of italian or am I missing something ?
I think your point is valid, it seems that languages differ over their liking for definite and indefinite articles. French needs them, English is more indifferent to them, and Russian seems to not need them at all. I dont know about Italian but assume is is closer to French in this regard. When these differences emerged and why is interesting. It is also interesting that languages tend to simplify over time; there are several theories why this should be the case. You would have thought that ancient languages would have been simpler, but they weren't.
As somebody who is familiar with 7 languages in total up to a certain extent, I can tell you - you are completely right. NOTHING would be lost leaving it aside. In Italian it's just something they have and it is something that makes the language sound more beautiful - try saying it aloud and you will see how it makes a melodic difference.
And this one might give you a shock, but we can go even further and dare to say, that French is superfluous too (aside from other aspects which make french a creepy and hard language), for example - you don't even really need articles at all (similar to how you omit them when you add "ton" or "ta"...)! Or sexes! (nouns/adjectives) Now if you are a French speaker you will think I'm telling you ❤❤❤❤❤❤❤❤, but really they are not needed, this information is in most cases superfluous and only in certain moments you could add the extra info where needed. But I can tell you that there are many languages which don't use articles or other things and they transfer information as good and maybe even more effectively, because you don't need la le before every word...