John 3:28

αὐτοὶ ὑμεῖς μοι μαρτυρεῖτε ὅτι εἶπον· οὐκ εἰμὶ ἐγὼ ὁ Χριστός, ἀλλ' ὅτι ἀπεσταλμένος εἰμὶ ἔμπροσθεν ἐκείνου.

Rough Word-by-word:
Yourselves you all to me you all witness that I said, "Not I am I the Christ, but that having been sent I am in front of him."

Smooth Translation:
You, yourselves, all witness to me that I said, "I myself am not the Christ, but that I have been sent in front of him."

αὐτοὶ intensive use of pronoun nominative plural masculine "yourselves"

ὑμεῖς pronoun nominative 2nd plural "you all"

μοι pronoun dative 1st singular "to me"

μαρτυρεῖτε verb present active indicative 2nd plural from μαρτυρέω (I testify/I witness) "you all witness"

ὅτι conjunction "that"

εἶπον verb aorist active indicative 1st singular from λέγω (I say) "I said"

οὐκ adverb of negation "not"

εἰμὶ verb present indicative 1st singular from εἰμί (I am) "I am"

ἐγὼ pronoun 1st singular "I"

ὁ definite article nominative singular masculine "the"

Χριστός proper noun nominative singular masculine "Christ"

ἀλλ' strong adversative conjunction "but"

ὅτι conjunction "that"

ἀπεσταλμένος verb perfect passive participle nominative singular masculine from ἀποστέλλω (I send) "having been sent"

εἰμὶ verb present indicative 1st singular from εἰμί (I am) "I am"

ἔμπροσθεν genitive preposition "before/in front of"

ἐκείνου demonstrative pronoun genitive singular masculine "of that one [man]/of him"