"Do you hear it?"
"Słyszeć" uses accusative.
Accusative of "to" is "to", "tego" is genitive.
You might have confused it with "słuchać", which uses genitive.
Yes, generally different verbs take different cases. Same goes for prepositions. Accusative is probably the most widely used case.
Czy slyszysz go?
Could be correct if we are talking about a neutral thing that makes a sound. RIght?
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.
Czy slyszysz to dziecko? Czy slyszysz go?
Would that be a possible case? Or would it be tego in this case even though it is not masculine?
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)
Why you prefer "to" to "je" which as far as I understand both can mean 'it' (in the accusative) ?
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.