The word play in this verse demonstrates why Jesus word's could not have been translated from Aramaic and why they are impossible to translate completely into English, Lots of interesting and unusual grammatical constructions here along with unique words , including one that creates that clever play on words that is lost in translation. Also there are several uncommon words.  Again, the use of unique vocabulary seems chosen for the sake of humor and word play that has to be explained because it cannot be translated. Plus, lots of words added in the KJV to make this read better but which may change its meaning.

The Greek word translated as "and 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.  Biblical translators change it to "and" when it doesn't contradict what Jesus said earlier, but here the contradiction is in the sentence itself.

There is no "when" in the Greek. The clause that begins the sentence is called a "genitive absolute", a genitive with an participle at the beginning of a sentence. The genitive noun (here, actually an infinitive with an adjective) acts as the subject and the participle as a regular verb. Confusing but this boils down to "while" rather than a "when". This dependent clause has a separate noun and verb than the main clause to describe things happening at the same time.

"These things" is an adjective that means "from here" or "this/that thing." It is not the pronoun, though very closely related. The form is neutral plural, which is where the "things" come from, the actual noun is the following word.

"Begin" is from a verb in the form of an adjective that means "to be first", "to begin," and "to make a beginning", "to rule", "to govern," and "to command."  This is the first word in the verse. The form is someone acting passively on themselves, so "they are starting themselves" or "they are commanding themselves".  At this point, we don't know what the noun is. The "these things" is not the true subject and it comes after the verb, not before, so "they".

The word translated as "to come to pass" means "to become," or, of events, "to happen",  that is, to enter into a new state. Though this is the infinitive of the verb, "to happen", it acts as the subject of a sentence. Infinitives introduced by an article, or in this case, a related adjective, act as a noun describing the verb's action. So "to happen" becomes "these happenings", following the plural form of the adjective.

There is no "then" here. This added because the initial phrase didn't start with "while". 

"Look up" is where the fun begins. This word is only used by Jesus here. It  means to "lift your head up", which is funny because the next clause says "left your heads up" in more common terms. It is used  because the other meanings of this word are, of people, "rise out of difficulties" and "breath again".  The word has a general sense of "keeping your heads above water". The "breath again" is a play on the earlier verse where the word translated as Luke 21:26, "hearts failing" actually means "to stop breathing".   The word is actually an even funnier given the context because it literally means "up from secret" (as in up from the depths), which gives the sense that people are hiding during these troubles.  Even the "pop back up" meaning of this word is funny.

The Greek word translated as "and" is used as the conjunction "and", but it also is used to add emphasis ("also").

"Lift up" is the more common verb that means "lift up" or "raise".

The word translated as "your" is plural addressing a group of Jesus's listeners.

The term translated as "head", it means "head" and "top" but also the completion of a thing (as we say, "bringing it to a head"). It is also a metaphor for life ("losing your head" in Greek doesn't mean an emotional outburst, but being killed).

"For" is another unique word that means "because", "for the reason that", and "since". Since Jesus commonly uses two other more common word to mean "for" and "because", it is hard to see why he uses this word here, unless he wants to draw attention to the special nature of the words in this verse.

The word translated as "your" is plural addressing a group of Jesus's listeners.

"Redemption" is yet another unique word that means "ransoming" "redemption by payment of ransom", and "deliverance".  This is actually, the punch line of the verse, the final word that has impact because it is saved to the end. The form is "that redemption of yours", which is Jesus's standard punch line construction. It is set up by the previous word, which appears after in the KJV. Jesus uses the root of this word  that means "ransom" only in two other places, (Matthew 20:28  and Mar 10:45)  and they absolutely fit with the meaning here.

The word translated as "draweth near" is a made-up verb form of an adverb "near" in space, time, and relationships. In English, we would say "nears" or, in the form here, "has neared," doesn't quite work so perhaps "has gotten close" or, in the case of time, "is nearly here."  What makes the use of this word funny is that it is most commonly used to describe the "the realm of the skies" or "the kingdom of heaven". Upon hearing it, Jesus's listeners would expect that phrase so "that ransoming of yours" comes as a surprise.