(The question comes from Collar and Daniell, Beginner's Latin Book, Exercise 50.2., p 17.) I know that portatne is carry in the present indicative third person singular, with the -ne indicating the sentence is a question, possibly translating to "what/who carries [...]". I know that dominō is the dative singular of dominus (master). I believe the use of dative here is the 'dativus commŏdi' (or at least that's what wikipedia tells me), indicating this is to be translated as "for the master". Vīnum et ova means wine and eggs, with vīnum being the accusative singular of vīnum and ova being the accusative plural of ovum. I assume this means the sentence in full translates to "What carries the wine and eggs for the master" Would a correct response be "Equus vīnum et ova portat dominō" or "Servus vīnum et ova portat dominō", or "The horse carries the wine and eggs for the master" and "The slave carries the wine and eggs for the master"?
You are right that -ne indicates a question, but it is only used for binary questions. If ille portat is "he carries", then portatne ille? is "does he carry?" — the expected answer is either "yes, he does" or "no, he doesn't", not "the horse carries". If you want to ask who or what carries, you should use quis or quid as the subject: Quis/quid portat vinum et ova? "Who/what brings wine and eggs?"
Your question does not have an explicit subject:
Portatne dominō vīnum et ova?
"Does he/she/it carry wine and eggs to the master?"
The implicit subject can be a horse, but without context I can't tell. Presumably the subject of the previous question(s) is repeated. For example, if you have this kind of pair of questions, it is clear that the subject is the horse:
Qualis est equus? — "What is the horse like?"
Portatne [ille] vinum domino? — "Does it bring wine to the master?"
But the implied subject could also be someone or something else. Some possible answers might be:
Ita vero, vinum et ova ei portat. — "Yes indeed, it brings wine and eggs to him."
Servus vinum et ova portat, non equus. — "The slave brings the wine and eggs, not the horse."
Ita (non) facit. — "It does (not do) so."
Vinum et ova domino non portantur. — "The wine and eggs are not brought to the master."