"To where do you make a journey?"
Translation:Quo vos iter facitis?
quo -> 'to where' (movement towards a location) -> "to where are we going?"/"Where are we going to?"
ubi -> 'where' (as in where something is, no movement) -> "Where are we?"
unde -> 'from where' (movement from a location) -> "From where are you coming?"/"Where are you coming from?"
Hope that makes sense.
Ubi does mean "where," in the sense of "located where."
Quo means "where" in the sense of "moving (to) where."
Not sure what you mean about "quo meaning what," though the ablative relative/interrogative pronoun (quo) can mean "WITH what" or "BY MEANS OF which," and so forth.
(The quo? / ubi? distinction, for the two types of "where?", is seen also in the difference between eo = (to) that place and ibi = in that place.
Ubi eo advenimus = when we arrive there . motion (to) there.
Ibi est caupona = there's an inn there . located there. )
Since vos is the plural subject-form, "you," the verb (facitis) ends in the plural "you (all)" ending -tis. The noun (direct object) iter, "journey", doesn't need to be plural, since all of you (in this sentence) are making a (singular) journey.
If all of you make journeys, plural, it would be: Vos itinera facitis.
Your dictionary must also include the relevant fact that iter, itineris is NEUTER, which (as Moopish explained) means that the nomin. and accus. forms are identical.
So, the 3rd decl. ending -em for accusative singular is specifically only for nouns (and adjs.) that are either masculine (like pater: patrem) or feminine (like arbor: arborem), but never for neuters.