"Do you hear it?"
Since słyszysz requires an accusative, and go is accusative of on, that would be a good translation if it/go was a non-animate thing or an animal of unknown sex of masculine grammatical gender in Polish.
A pretty rare situation, and therefore while it makes total sense in some contexts, I think Duolingo shouldn't accept it for educational reasons.
that is complicated question
go is :
accusative=genitive form of on, used in not accented position in a sentence
genitive form of ono, used in not accented position in a sentence
tego is :
genitive form of to = this/that/these/those in all sentences when it's not followed by a noun
genitive form of to=this when followed by neuter noun (or meaning "this one" and implying neuter noun)
genitive form of ten=this when followed by masculine not animated noun (or meaning "this one" and implying masculine not animated noun)
genitive=accusative form of ten=this when followed by masculine animated noun (or meaning "this one" and implying masculine animated noun)
It's hard to decide what to use without context. "to" is the dummy pronoun, and makes most sense if you don't know what 'it' is.
But if you know what 'it' refers to (when it's similar to Do you hear him/her), then you take into consideration 'its' grammatical gender. So let's say that we were talking about... a wounded animal. The phrase "ranne zwierzę" is neuter. Therefore you would use "Słyszysz je?" indeed in such a case.
"to" and its forms work for anything in "Do you hear [it/this/that]?", often when you don't know what 'it' is.
"go" is technically a form of "on", so the first thought when I see "Słyszysz go?" is "Do you hear him?".
However, as all nouns in Polish have a grammatical gender, this will also work for "Do you hear it?" if only this "it" is known and it's masculine singular in Polish.
For example "Mój brat ma bardzo głośny komputer. Słyszysz go?" is "My brother has a very loud computer. Do you hear it?".
Anyway, your suggestions is correct. Added now.
First I answered "czy słyszysz to?" to this and it said that it was "słyszycie to". So it said that I was incorrect because I used the singular you and not the plural you, when I couldn't possibly have known that they meant that.
Next time, I answered "czy słyszycie to?" and it said that it was "słyszycie to?" so I was wrong for saying "czy"
After asking my Polish partner, who agreed that i was right on both occasions, I came to this comment section and it said that the correct answer was in fact "słyszysz to?"
These alternative answers should be included as correct answers.
An average native speaker won't be as strict as the people that want to teach you the language. The problem we have with "Czy [słyszysz/słyszycie] to?" is that it ends with a pronoun although you have another place to put it.
Correcting you from "Czy słyszysz to?" to "Słyszycie to?" was surely confusing, but I'm afraid that's how the algorithm works, it (usually) corrects you to the main answer (the one someone put as the default) even if there is a correct answer closer to yours.
The best answers here are "[Słyszysz/Słyszycie] to?", with "Czy [ty to słyszysz/wy to słyszycie]?" being good as well, plus actually just "[Słyszysz/Słyszycie]?" without 'to' are also quite likely.