John 1:19

Καὶ αὕτη ἐστὶν ἡ μαρτυρία τοῦ Ἰωάννου, ὅτε ἀπέστειλαν οἱ Ἰουδαῖοι ἐξ Ἱεροσολύμων ἱερεῖς καὶ Λευείτας ἵνα ἐρωτήσωσιν αὐτόν· σὺ τίς εἶ;

Καὶ conjunction "and"

αὕτη demonstrative pronoun nominative feminine singular "this"

ἐστὶν verb present indicative 3rd plural from εἰμί (I am) "she is" (note: the feminine here and on the pronoun because the antecedent is μαρτυρία which is feminine. The English translation will not use the feminine)

ἡ definite article nominative feminine singular "the"

μαρτυρία noun nominative feminine singular "testimony"

τοῦ definite article genitive masculine singular "the"

Ἰωάννου proper noun genitive masculine singular "of John"

ὅτε adverb "when"

ἀπέστειλαν verb aorist active indicative 3rd plural from ἀποστέλλω (I send) "they sent"

οἱ definite article nominative masculine plural "the"

Ἰουδαῖοι proper noun nominative masculine plural "Jews"

ἐξ preposition genitive "from/out of"

Ἱεροσολύμων proper noun genitive plural "Jerusalem" (hmmm...why is this plural?)

ἱερεῖς noun accusative masculine plural "priests"

καὶ conjunction "and"

Λευείτας noun accsative masculine plural "Levites"

ἵνα conjunction subjunctive "that"

ἐρωτήσωσιν verb subjunctive active indicative 3rd plural from ἐρωτάω (I ask) "they might ask"

αὐτόν pronoun accusative masculine singular "him"

σὺ pronoun nominative 2nd person singular (predicate nominative) "you"

τίς pronoun nominative masculine singular "who"

εἶ verb present indicative 2nd singular from εἰμί (I am) "you are"

Rough Word-by-word:
And this she is the testimony the of John when they sent the Jews from/out of Jerusalem priests and Levites that they might ask him you who are

Smooth Translation:
And this is the testimony of John when the Jews sent priests and Levites from Jerusalem that they might ask him, "Who are you?"