The pronoun τις is sometimes put for the relative; as in Latin qui and quis, and in English, who is both relative and interrogative. Examples,
(1) Where τις retains its interrogative meaning, and still must be rendered in Latin by quis or quod. E.g. Mat 20:22
αποκριθεις δε ο ιησους ειπεν ουκ οιδατε τι αιτεισθε δυνασθε πιειν το ποτηριον ο εγω μελλω πινειν και το βαπτισμα ο εγω βαπτιζομαι βαπτισθηναι λεγουσιν αυτω δυναμεθα
But Jesus answered and said, “You do not know what you are asking. Are you able to drink the cup that I am about to drink?” They said to Him, “We are able.”
respondens autem Iesus dixit nescitis quid petatis potestis bibere calicem quem ego bibiturus sum dicunt ei possumus
And Jesus answering, said: You know not what you ask. Can you drink the chalice that I shall drink? They say to him: We can.
(2) Where τις is equivalent to ει τις; as in 1 Cor 7:18
1 Corinthians 7:18
περιτετμημενος τις εκληθη μη επισπασθω εν ακροβυστια τις εκληθη μη περιτεμνεσθω
Was any man called when he was already circumcised? He is not to become uncircumcised. Has anyone been called in uncircumcision? He is not to be circumcised.