Determiners are words that identify or quantify a noun. Relative determiners express a relationship or quantify the noun by comparing the noun with another object. (example: “of what sort”, “as great as” , “as far as”, “who”, “which”
ἦν δὲ σάββατον ἐν ᾗ ἡμέρᾳ τὸν πηλὸν ἐποίησεν ὁ Ἰησοῦς καὶ ἀνέῳξεν αὐτοῦ τοὺς ὀφθαλμούς. John 9:14
ēn de sabbaton en hē hēmera ton pēlon epoiēsen ho Iēsous kai aneōxen autou tous ophthalmous.
it was now sabboth in which day the clay he made the Jesus and he opened of him the eyes.
Now it was the Sabbath day when Jesus made the mud and opened his eyes.
ῇ is a relative personal pronoun that is a determiner. It determines or identifies the day in which Jesus opened the blind man’s eyes. It was the Sabbath day.