Do -- - This English helping verb is used to create questions, commands, negative statements, and smooth word flow in translation from Greek This word is inserted to negate a verb that doesn't exist in the Greek.

n't --  (WP) The negative "not" used here is the Greek negative of a subjective opinion, commands, and requests. This negative appears before the participle, "coming" or "showing up." In Greek, the negative negates the following word, or, the whole clause when it is before the verb.  The negative doesn't mean that he doesn't show up, but that you "don't want him coming.:

let - (IW) This verb does not exist in the source. There is not command to the listeners.

him -- (WF) This is from the third-person, singular form of the following verb. It is a subject, "he" not an object "him.

missing "should" or "might"-- (MW) A helping verb is necessary because the following verb is a verb of possibility, a subjunctive, something that "should" or "might" occur. The helping verb is not needed in a clause beginning with an "if," "when," "whoever" and other conditional clauses.

find -- The term used for "he find" is the source of our word, "heuristic," meaning enabling a person to find out something for themselves. It means "find out" and "discover."  The form is one of possibly happening at some time, "might discover."

you -- The "you" here is plural, indicating it was addressed to a group of Christ's listeners as the object, "you all".  There is a sense that the problem isn't want person sleeping but everyone in the group.

sleeping. -- The Greek word translated as "sleeping" means "to lie down to sleep", "to sleep," and "to lie asleep." The form is that of an adjective, "sleeping".

when -- (IW) There is no Greek word that can be translated as "when" in the Greek source. While the "when" indicates something that might happen, that is not the word used here.

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

arrives -- (WF) The word translated as "comes" primarily means "to start out" but Christ usually uses it to mean "come" but not always. It indicates movement, especially its beginning, without indicating a direction toward or away from anything, so it works either as "come" or "go," but it is more like our phrase "being underway." Our English word "show up" captures both the "start" and "come" ideas.  The form is an adjective, "showing up".

without warning, -- (WW) The adverb translated as "without " is unique for Jesus to use. It is spelled in an uncommon way. The meaning is "at a moment."