"Where is his destination", with the stress falling on the word "is", asks for the location of an unfamiliar place name. Say he was going to Motueka. Where is his destination? It's west of Picton, in the South Island of NZ.
There is an exact English translation of "ke mana", i.e."whither", so an accurate translation is "Whither his destination?" (No verb required.) Not current usage, exactly, but at my age I think I should be indulged.