I think the Swahili is OK here, and represents one way of saying that Serengeti is where you will find zebras, but it is not to be translated word-for-word. And that's why I don't like the English translation. I think I could ask (in Kenya): Wapi naweza kumwona twiga? and the answer could be "Twiga utamwona Tsavo." It is understood that we are not talking about any particular giraffe.
Wapi would usually go at the end of the sentence (unless you make a cleft sentence with a relative phrase), and if you say kumwona, it makes it much more likely that the listener will think you really mean one singular, specific giraffe ("the giraffe"). Object prefixes are not exactly a sign of definiteness, but they are more likely if the object is definite.
Ninaweza kuona twiga wapi?
Ni wapi ninapoweza kuona twiga?
I agree with you on the placement of wapi. As far as object infixes, I feel uncomfortable not using one when the direct object is a person or animal. I'm not sure where that comes from -- maybe the native speakers I used to interact with, maybe just a misconception on my part.