Translation:How many passengers are boarding that bus?
“Boarding that bus” means “getting on that bus.” If what we're saying is that they've already boarded and are using the bus for transporation, then the word should be “riding that bus.” You drive a bus when you're the person behind the wheel, but the rest of those on board can be referred to as “riding” it.
On the other hand, doesn't "naik" refer to the action of stepping up on to the bus. I get that it's kind of idiomatic, but "boarding" does keep that sense.
Elsewhere, I believe 'naik' can be translated as 'take' (I take the bus) so could this not be 'How many passengers take that bus?'
"naik" in this case can mean both "boarding" and "riding". In addition "naik" in this context (i.e., "bus") can also mean "taking".
The pronunciation of"bus" in Indonesian is off here. Supposed to be "boos" not "bis"
Edit: It can be either way, "boos" or "bis". Sorry. Just watched an Indonesian movie :)
I struggled with this too. I agree with the other comments that "naik bus" (which can be both spelt and pronounced "naik bis") can be translated as, "board the bus" "travel on the bus" "go by bus" "take the bus"....