Uter can be a question but it refers to two (people, things etc.) In these example sentences, two people / things are being discussed even if English does not always convey that.
Uter poēta ā plūribus legitur? │ Which poet / which of the two poets is read by most people?
Uter vestrum mēcum veniet? │ Which of you (two) will come with me?
Sed uter vostrōrum est advectus mēcum nāvī? (Plautus) │ But which of you was brought here in the ship with me?
Utrī hōrum mortālium amīcī sunt dī, utrī inimīcī? │ To which of those [two] mortals are the gods friendly and to which unfriendly?
Utrum cōnsulem Carthāginiēnsēs interfēcērunt? │ Which consul / which of the two consuls did the Carthaginians kill?
Utram hārum vīs condiciōnem accipe (Plautus) │ Whichever condition of these two you prefer, take it.
Uter also has the indefinite sense of whichever (of the two), either one or the other
Et pater et fīlius bene dīcunt. Vōcem utrīus nunc audīmus? │ Both the father and the son speak well. Do we now hear the voice of either of them?
The famous incident which sparked the 2nd Punic war: a Roman ambassador offered the Carthaginians a choice of war or peace, symbolized by the folds of his toga, and we know which choice the Carthaginians made.
tum Rōmānus sinū ex togā factō 'Hic' inquit 'vōbīs bellum et pācem portāmus: utrum placet, sūmite' (Livy)
Then the Roman, gathering up his toga into a fold, said, “We bring you here both war and peace; choose which you will! [ = whichever of the two pleases]”
Exercises: Complete the Latin sentences with the appropriate form of uter: bear in mind that, even if English does not explicitly state it, uter is [1] asking which (of two) or [2] stating either or whichever
[i]
[1] Which book do you want? │ _____ librum vīs?
[2] Which law is older? │ _____ lēx est antīquior?
[3] In which cottage is Julia? │ In _____ casā est Iūlia?
[4] To which boy did you give the book? │ _____ puerō librum dedistī?
[5] Which of (the two of) us is wealthier? │ _____ igitur est divitior? (Cicero)
[6] Which camp did Caesar capture? │ _____ castra cēpit Caesar?
[7] Which (of the two groups of) soldiers do you prefer? │ _____ mīlitēs māvīs?
[8] Which of (the both of) us, therefore, is more covetous of a smart saying? │ _____ igitur nostrum est cupidior dictī? (Cicero)
uter; uter; utra; utra; utrā; utrī; utrōs; utrum
[ii]
[1] Your troops will never capture either man there. │ Cōpiae vestrae _____ virum ibi numquam capient.
[2] If either wants it, I shall assign assessors. │ Sī _____ volet, recuperātōrēs dabō. (Cicero)
[3] Nevertheless, the confusion of the names remained famous in the story of which people the Horatii were, and of which people the Curiatii were. │ Tamen in rē tam clāra nōminum error manet, _____ populī Horātiī, _____ Curiatiī fuerint (Livy)
[4] if you can learn which of the two was attacked by the other │ sī scīre ... possīs, _____ ab _____ petītus ... sit (Livy)
[5] that we two may show by the outcome which people is the superior in war │ ut noster duōrum ēventūs ostendat _____ gēns bellō sit melior (Livy)
uter; uter; utra; utrīus; utrīus; utrō; utrum
____________________
[i]
[1] Utrum librum vīs?
[2] Utra lēx est antīquior?
[3] In utrā casā est Iūlia?
[4] Utrī puerō librum dedistī?
[5] Uter igitur est divitior?
[6] Utra castra cēpit Caesar?
[7] Utrōs mīlitēs māvīs?
[8] Uter igitur nostrum est cupidior dictī?
[ii]
[1] Cōpiae vestrae utrum virum ibi numquam capient.
[2] Sī uter volet, recuperātōrēs dabō.
[3] Tamen in rē tam clāra nōminum error manet, utrīus populī Horātiī, utrīus Curiatiī fuerint
[4] sī scīre ... possīs, uter ab utrō petītus ... sit
[5] ut noster duōrum ēventūs ostendat utra gēns bellō sit melior
