Let's talk about a little expression that is useful in various situations. It's made up of just three words but it is easily expanded, since sometimes you just want a phrase to stand out in some way by adding words. The expression is Che ne so.
Let's unpack it.
Che can mean "that" or "what." In this case, it's "what," as when it is part of a question.
Ne is a particle that can stand for several things, such as "about it," "of it," "from it" and more. If ne is unfamiliar to you, or you don't know how to use it comfortably, check out Marika's lessons about this particella.
So is the first person singular of the verb sapere (to know).
As you have likely discovered, Italians, rather than just saying the equivalent of "I know," usually say "I know it:" Lo so, or when it's negative, non lo so (I don't know it). But in today's expression, lo (just plain "it") is replaced by ne (about it).
Since the expression is short, the personal pronoun io (I) is often added for emphasis. It doesn't add anything grammatically, but it makes it more personal. In addition, it is often preceded by e (and). Even though e means "and," it's often the equivalent of "so." Sometimes it doesn't really mean anything.
Che ne so io? or Io, che ne so? The pronoun io can go either at the beginning or the end of the expression. This is the equivalent of "How should I know?" "What do I know?" "How would I know?" The following example is one of the most common versions of this expression. Italians don't always think of this expression as being a true question so they don't necessarily use a question mark.
Addò [dove] sta Saverio? -E che ne so.
Where's Saverio? -How do I know?
Captions 14-15, Ma che ci faccio qui! Un film di Francesco Amato - Part 10
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Pasquale, chi è tutta questa gente? -E che ne so, dotto' [dottore]? Qua pare tutti i poveri di Napoli,
Pasquale, who are all these people? -And how should I know, Doc? Here it seems like all the poor people of Naples
Captions 6-7, Moscati, l'amore che guarisce EP 2 - Part 12
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Lojacono is looking for one of the residents of an apartment building and asks the local busybody:
Sa mica se Giacomo Scognamiglio è in casa? -E che ne so, Commissa'?
You don't happen to know if Giacomo Scognamiglio is home? -And how should I know, Chief?
Captions 67-68, I Bastardi di Pizzofalcone EP 3 Vicini - Part 7
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In the following example, Marcello, who is not a very smart guy, but is trying his best, suggests taking a selfie together with the policemen who come to check on Michele (the father of his girlfriend) who is under house arrest.
Oh, ma che so o famo [romanesco: ce lo facciamo] un selfie insieme?
Oh, I don't know, shall we take a selfie together?
Caption 20, Liberi tutti EP3 Quanto è libero un fringuello? - Part 6
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Instead of adding a word, he removes one: ne. It's colloquial and likely Romanesco, and lots of people say it this way. Che so?
Even though we have explained each word, the expression is often merely a way of saying "I don't know," especially when you are making a suggestion, as Marcello is doing. Some people might use the word magari in the same kind of situation. It's just an intercalare (a filler word or expression). Here's an example.
Perché, diciamo... -comunque devono sostenere il peso. -Devono sostenere il peso, più che altro devono fare, che ne so, la stessa cosa per un'ora.
Because, let's say... -anyway they have to support the weight. -They have to support the weight, more than that, they have to, I don't know, do the same thing for an hour.
Captions 50-51, Francesca Cavalli - Part 2
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Here, Che ne so is paired with magari for making a suggestion.
Che ne so, magari stasera a cena? -Può darsi.
I don't know, maybe tonight for dinner? -Maybe.
Caption 93, Il Commissario Manara S1EP8 - Morte di un buttero - Part 2
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Although the expression is commonly used in the first person, it can also be a valid question to someone else, and is more literal in this case.
Eh, quando un uomo si innamora, si dimentica di tutto. -Tu che ne sai? -Così dicono tutti.
Uh, when a man falls in love, he forgets everything. -What do you know? -That's what everyone says.
Captions 38-39, Moscati, l'amore che guarisce EP1 - Part 11
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When you are thinking of what to cook for dinner, what to watch on TV, where to go on a Sunday afternoon, or what to give a friend as a birthday present, try suggesting it in Italian, and throw in a little "che ne so" as you would "I don't know." Have fun with it!