John 8:18

ἐγώ εἰμι ὁ μαρτυρῶν περὶ ἐμαυτοῦ καὶ μαρτυρεῖ περὶ ἐμοῦ ὁ πέμψας με πατήρ.

Rough Word-by-word:
I I am the one testifying concerning myself and he testifies concerning me the one sending me father.

Smooth Translation:
I myself am the one testifying concerning myself and the father who sent me testifies concerning me.

ἐγώ pronoun nominative 1st singular "I"

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

ὁ definite article nominative singular masculine "the"

μαρτυρῶν present active participle nominative singular masculine from μαρτυρέω (I testify) "one testifying"

περὶ preposition with genitive "concerning"

ἐμαυτοῦ reflexive pronoun genitive singular masculine "myself"

καὶ conjunction "and"

μαρτυρεῖ verb present active indicative 3rd singular from μαρτυρέω (I testify) "he testifies"

περὶ preposition with genitive "concerning"

ἐμοῦ pronoun genitive 1st singular "me"

ὁ definite article nominative singular masculine "the"

πέμψας aorist active participle nominative singular masculine from πέμπω (I send) "one who sent"

με pronoun accusative 1st singular "me"

πατήρ noun nominative masculine singular "father"