If -- The "if" here expresses a condition but it means nothing regarding whether that condition is met or not. It also means "if ever" and "whenever."

thou -- This is from the second-person, singular form of the verb.

knewest  --- The verb translated as "knewest" means "to see" but it is used like we use the word "see" to mean "to know" or "to perceive." In th KJV, it is almost translated as many times as "know" as it is "see." It is in the pluperfect tense, which occurs rarely. It corresponds to the sense of the English pluperfect, which indicates an event viewed as having been once and for all accomplished in past time.

the -- The word translated as "the" is the Greek definite article, without a noun, it has the sense of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more. 

gift  - The word translated as "gift" has the broader sense of "bounty" and indicates a strong sense of generosity, that is, that the things that are given freely.

of -- This word "of"  comes from the genitive case of the following word that requires the addition of a preposition in English.  The most common is the "of" of possession.

missing "the"  -- (MW) The untranslated word is the Greek definite article, 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. 

God,  -- The word translated as "God" means "God" and "deity." It is introduced with an article, so "the God," "the Divine" or "the divine one." Jesus often uses it this way perhaps to indicate the one God as opposed to the pagan gods.

and -- The Greek word translated as "and" is used as the conjunction "and," but it also is used to add emphasis ("also"). In a series, it is can be translated as "not only...but also." After words implying sameness "as."

who  -- The word translated as "who" means primarily "anything" or "anyone," but Jesus often uses it to start a question so it means "who," "what," or even "why."

it is -- The verb "is" here is the common form of "to be" in Greek. It means to have a certain characteristic or remain in a certain condition. It also equates terms or assigns characteristics.  When the verb "to be" appears early in the clause before the subject, the sense is more like "it is" or, in the plural, "there are."

that -- The word translated as "that" is a demonstrative pronoun ("this" "that"), but it often acts as a pronoun ("the one that), especially a connective pronoun ("the one that") introducing a dependent clause.

saith -- The word translated as "sayeth" is the most common word that means "to say," and "to speak,"  but when used with an objective noun or pronoun, the sense is "say of" or "speak of." 

to -- This word "to" comes from the dative case of the following word that requires the addition of a preposition in English. The most common is a "to" for the English indirect object.

thee, -- The word for "you" is the indirect object form of the singular, second-person pronoun in the form of an indirect object, which usually requires a preposition in English, like "to you."

Give -- The verb translated as "give" means "to give," "to grant," "to hand over," "appoint," "establish," and "to describe." It is almost always translated as some form of "give."

me -- The "me" is in the indirect object form on the first-person pronoun, so usually "to me," though the form has other uses in Greek.

to -- This "to" is added because the infinitive form of the verb requires a "to" in English.

drink; -- The word "drink" is the Greek for meaning to "drink." It also has a double meaning. "To drink" also means "to celebrate."

thou -- This is from the second-person, singular form of the verb.

wouldest  - The particle translated as "wouldest" describes a limitation of circumstances. While it can mean "would" in the sense of a person having a choice, it might be better translated here as "could" since the limitation is one of ability, that is, the ability to perceive. The sense of this verse in Greek is almost wistful, if you could only seen the situation as the opportunity of a lifetime, you could have made so much more of it.

have -- (WT) This helping verb "have" indicates that the verb is the tense indicating an action completed in the past. This is not the tense of the verb here.

asked -- The Greek word translated as "asketh" means "ask" but has shades of meaning from "demand" to "claim." It means to beg or even to demand something from someone else.

of -- (IW) There is nothing that can be translated as "of" in the Greek source.

him, -- The word translated as "him" is the Greek word commonly translated as third-person pronouns in English.  The word means "the same" when used as an adjective. In the adverbial form, it  means "just here" or "exactly there." This pronoun follows the noun so "of his."

and -- The Greek word translated as "and" is used as the conjunction "and," but it also is used to add emphasis ("also"). In a series, it is can be translated as "not only...but also." After words implying sameness "as."

he -- This is from the third-person, singular form of the verb.

would - The particle translated as "would" describes a limitation of circumstances. While it can mean "would" in the sense of a person having a choice, it might be better translated here as "could" since the limitation is one of ability, that is, the ability to perceive. The sense of this verse in Greek is almost wistful, if you could only seen the situation as the opportunity of a lifetime, you could have made so much more of it.

have -- (WT) This helping verb "have" indicates that the verb is the tense indicating an action completed in the past. This is not the tense of the verb here.

given  -- The verb translated as "given" means "to give," "to grant," "to hand over," "appoint," "establish," and "to describe." It is almost always translated as some form of "give."

thee -- The word for "you" is the indirect object form of the singular, second-person pronoun in the form of an indirect object, which usually requires a preposition in English, like "to you."

living - -- The verb means "live," "to be alive,” “to be full of life," "to be strong," and "to be fresh." So it is life in the sense of having a vital life, strong and growing. Perhaps in English, “thrive” would be more precise.

water. . -- "Water" is the noun that means "water," "spring water," "drinking water," "rain water," "rain," "time running out" (from the water clocks used in courts),  "liquid," the constellation Aquarius, the winter solstice, and a place with mineral waters.