But -- The Greek word translated as "but" means "but," "however," and "on the other hand." It joins phrases in an adversarial way. Since it always falls in the second position, translating it as "however" often captures its feeling better.  It can also be an explanation of cause ("so").

since -- (WW) The "since " here expresses a condition but it means nothing regarding whether that condition is met or not. It also means "if ever" and "whenever." It does not mean "since."

you -- This is from the second-person, plural form of the verb.

do -- This helping verb is used to create questions, commands, negative statements, and smooth word flow in English, but the Greek could be either a question or a statement.

not -- The Greek word translated as "not" is the Greek negative used to deny objective facts, not opinions. It means "no," "not," or"no truly." It makes a negative statement of fact. Adding "really" to the sentence captures the same idea. When a negative precedes the verb, it affects the whole clause. When it precedes other words, its force is limited to those words.

believe --  The Greek word translated as "believe" does not apply to religious belief as much as it does trusting in other people, especially their word. Christ usually uses it in contexts, as the one here, that apply to trusting words. The negation of "belief" with the objective, instead of subjective, negative, equates trust with a fact. someone's words", "to comply", "to feel confident in a thing," and "to entrust in a thing."

what  -- (WW) This word should be the Greek definite article, "the," which usually precedes a noun and, without a noun, takes the meaning of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more.  It

he --  (WW) The word translated as "his" is an adjective that highlights its noun as being in a specific place or time from a word that means "there." Used a pronoun, the sense is "that one there." It is not the normal pronoun. It is not in the form of a subject, but a possessive.

wrote, - - (WW) "Wrote" is not from the common verb that means "wrote" but it is a noun that is Greek for "drawings", "a letter," (as in an alphabet) "diagrams," and "letters" (as in correspondence).

how -- "How" is the adverb that means "how," "by any means," and "I suppose." This is a common interrogatory pronoun used by Jesus.

are - This word is a helper verb to make a progressive form of the future tense.

you -- This is from the second-person, plural form of the verb.

going to -- (WW) This helping verb "going to" should not indicate the future tense, but that the verb describes a possibility, the subjunctive voice of the verb. A "might" or "should" in English is more appropriate, but is assumed in an "if/when/whoever/except" clause. Helping verbs are not needed in Greek since the main verb carries this information in its form.

believe -- The Greek word translated as "believe" does not apply to religious belief as much as it does trusting in other people, especially their word. Christ usually uses it in contexts, as the one here, that apply to trusting words. The negation of "belief" with the objective, instead of subjective, negative, equates trust with a fact.

 what -- (WW) This word should be the Greek definite article, "the," which usually precedes a noun and, without a noun, takes the meaning of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more. 

I -- (WF) "I" is the regular first-person adjective in Greek indicating possession, so  "mine," "of me," "my," "relating to me," and "against me." It is not the subject "I."

say?  -- (WW)  The Greek word translated as "words" is not logos, the Greek word that is almost always translated as "word(s)" in the Gospels, but another word which specifically means spoken words, that the English word "remarks" come from, and it captures this idea well. It is not a verb and has no relation to any of the verbs meaning "to say,"