For --The word translated as "for" introduces a reason or explanation so "because" and, in questions, "why." However, since this word always appears in the second position, it is more like an aside remark like, "consequently" or "as a cause." 

as- "As" is from a Greek word that means which means "even as," "how," and, in relating to time, "as" and "when."

Jonas -"Jonas" is from the Greek spelling of the proper name "Jonah."

was -- (CW ) The word translated as "was" means "to become," that is, to enter into a new state. When applied to events, this word means "to happen," "to occur," or "take place." For things, it can be "to be produced." When the participle takes a predicate, the sense is "coming into" something. The form of the verb's object can indicate the time or to whom it "happens." This is not the specific meaning of the word in this situation.

a -- There is no indefinite article in Greek, but when a noun doesn't have a definite article, the indefinite article can be added in English translation.

sign - "Sign" is Greek word that means a "mark," "sign," or "proof." The word in Greek is used specifically to means a sign from the gods and it that sense, it means "omen," "portent," and "constellations," but it also means a "proof" in reasoning. The translation of "proof" often seems how Jesus uses it.

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

the -- The word translated as "the" is the Greek definite article, "the," which usually precedes a noun or changes the word it precedes (adjective, infinitive, participle, etc.) to act like a noun. The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more. 

Ninevites, - - "Ninevites" is from the Greek form of the kingdom's name from the story of Jonah.

so-- The word translated in KJV as "thus" is in its adverbial form, so it means "in this manner," "so much," or "in this way."

shall -- This helping verb "shall" indicates that the verb is the future tense. Helping or auxiliary verbs are needed to translate the Greek verb forms into English.

also -- The Greek word translated as "also" is used as the conjunction "and," but it also is used to add emphasis, "even," "also," and "just."

the -- The word translated as "the" is the Greek definite article. The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more. 

Son -- The word translated as "son" more generally means "child" or "descendant." The phrase "the son of man" is the common way Christ refers to himself. It is discussed in detail in this article. Its sense may be "the child of the man."

of -- This word "of"  comes from the genitive case of the following word that required the addition of a preposition in English.  The most common is the "of" of possession, but it can also mean "belonging to," "part of," "which is," "than" (in comparisons), or  "for," "concerning" or "about" with transitive verbs. 

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.

man - The Greek word for "man" means "man," "person" and "humanity" in the singular. In the plural, it means "men," "people," and "peoples." 

be -- The verb "be" 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.  The word also means "to exist" and where it doesn't connect to characteristics or conditions.

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

this -- The "this" is a pronoun that can mean "this" or "that," the nearer,  "here," or "there,"  the further depending on usage. It often  follows the noun so it repeats the idea of the noun as "this one." .

missing "the/this"  -- (MW) The untranslated word is the Greek definite article," the," which usually precedes a noun or changes the word it precedes (adjective, infinitive, participle, etc.) to act like a noun. The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," and "those"). See this article for more.

generation. -- The word translated as "generation" means "race," "family," and "generation." The sense is a "type" or a "specimen" of a particular type.   Jesus uses it to refer to a type of person, specifically those like the Pharisees. His first describes this type earlier in Matthew as children who insist that everyone dance to their tune. His favorite adjectives describing of this type is "evil and adulterous," which in Greek, is closer to "worthless and cheating." In one previous discussion of this type, he compares them unfavorably with the people of Nineveh reacting to Jonah, and the queen of Sheba reacting to Solomon.