OK. I just talked to my friend from Italia and she says that in Italian, the two are equal. You just know from the context what you're trying to say. and in regards to my other suggestion "...all'idraulico", that is totally wrong and, in her words, "sbagliatissimo".. So forget that one. haha
That's why Google translate is unreliable... "Cosa fa l'idraulico mangia" makes no sense in Italian.. I think it's either an intonation difference, a context situation, or it could be that you have to add a personal "a" before l'idraulico:
Cosa mangia all'idraulico?! = What is eating the plumber?!
HOWEVER, I'm not sure.. I'm going to research it and get back to you..
This is a great question!!
Because Italian uses a different sentence structure when the sentence starts with a question word (cosa, quanto, quello, etc).
Normally Italian sentences go: subject (l'idraulico) - verb (mangia) - object (if there is an object eg. il cibo). "L'idraulico mangia il cibo"
When you add a question word to the front, the structure of the sentence changes to: question word (cosa) - verb (mangia) - subject (l'idraulico). "Cosa mangia l'idraulico?"
It's reasonably common for languages to change their sentence structure for questions. In English we don't change the order but we add an extra word (as well as adding the question word) - Compare "The plumber eats." with "What does the plumber eat?"
No, that's not a correct translation.
The Italian sentence is a question, not an affirmation while the English "what the plumber eats" that you wrote is more like a affirmative clause, which corresponds to "la cosa che l'idraulico mangia", the thing that the plumber eats.
Spiacente to sound like an idioto but, what is the difference between qual and cosa, they both mean what, correct? Is there a proper usage for each? Earlier lesson had "qual è il tuo totale" (what is your total) so couldn't this be "qual (instead if cosa) mangia l'idraulico"
For the most part, Qual corresponds to the idea of Which (one out of many) , while Cosa corresponds to What.
Here, I think Qual instead of Cosa would sound very strange.
Think about this English sentence:
Which do you study?
If you haven't introduced a context, to be clear what you're talking about, that would be wrong.
You would either say What do you study?, or you would need another thing there: - Which one do you study? - Which animal do you study? - Which of these do you study?
Oh, and qual is just a version of *quale, used before singular forms of essere that start with e:
Indicative Present - qual è
Indicative Imperfect - qual ero - qual eri - qual era
Back to our sentence, you would be able to use quale (or quali for plural) next to something, as a determiner: Quale piatto mangia l'idraulico ? = Which dish does the plumber eat? Meaning, which of the dishes (one out of a given group). Quali donne sono partite ? = Which women left?
Qual is useful for identifying one item from a group:
Qual è il tuo piatto ? = Which is your plate? (Which one of these is yours?)
Other than that, there are indeed cases where Qual means what :
Qual è il tuo indirizzo ? = What's your address? (you're probably asking the person to tell you what it is, not to identify it from a bunch of addresses).
More explanations about qual: https://forum.duolingo.com/comment/22637554/Quale-or-Qual-in-Italian-When-to-use-which
Qual, che, and cosa: https://www.italymadeeasy.com/ask021/