This is the 3484th most frequent Turkish word.
nereye
"Where to" (used to ask about a destination).
In this sentence, 'nereye' is used to ask for the destination of an action.
Nereye gidiyorsun?
Where are you going?
Here, 'nereye' is used in questioning the destination of a subject, 'this bus'.
Bu otobüs nereye gidiyor?
Where is this bus going?
In this case, 'nereye' is incorporated into a subordinate clause indicating uncertainty about a destination.