Three common noun endings are -ment, -tion, and -ity.

No, the contraction should've is a verb, a shortened form for the verbs 'should' and 'have'.
The contraction functions in a sentence as a verb or auxiliary verb.

Example:
We should have planned a little better.
We should've planned a little better.

A noun is a word for a person, a place, or a thing.
Example:
Jack and Jill were late. The traffic was terrible. (the nouns 'Jack and Jill' are words for people; the noun 'traffic' is a word for a thing)

A pronoun is a word that takes the place of a noun in a sentence.
Example:
Jack and Jill were late. They should have planned a little better. (the pronoun 'they' takes the place of the nouns 'Jack and Jill' in the second sentence)

The word "capitol" can be both singular and plural. "Capitol" typically refers to a specific building where a legislative body meets, such as the United States Capitol in Washington, D.C. When referring to multiple such buildings or multiple chambers within a building, you can use "capitols."

Yes, "students" is a plural noun that refers to individuals who are actively engaged in learning at a school or other educational institution.

"German submarine" is a common noun. It refers to any submarine manufactured or operated by Germany, not to a specific individual entity.

"Reputation" is a noun because it refers to a person's or thing's standing or status. You can determine its part of speech by looking it up in a dictionary, which will provide its grammatical category.

"Thinks" is a verb. It is the present tense form of the verb "think," which is an action indicating the process of using one's mind to form thoughts or opinions.

"He" is used as a subject pronoun, such as in "He is going to the store." "Him" is used as an object pronoun, such as in "I gave the book to him."

Yes, "trouser" is a noun. It refers to a garment covering the body from the waist to the ankles, with a separate part for each leg.

Yes, customers is a plural noun.

When you say customers, you are referring to more than one customer.

No, the word 'picked' is the past participle, past tense of the verb 'to pick'. The past participle of the verb is also an adjective, for example the picked apples, the pickedcontestants, etc.

The word "passel" is singular. It is used to refer to a large group or quantity of something.

To clarify, please provide more context or detail about what noun is missing in order to assist you effectively with your question.

The noun 'potato' is a singular, common, concrete noun; a word for a vegetable, a thing.

The noun 'coleslaw' is a common, concrete, uncountable noun; a word for a food, a thing.

No, "didn't" is a contraction of "did not," which is a verb phrase. It is not a noun.

For names ending in "s," it is a matter of preference whether to add an apostrophe followed by "s" ('s) or just an apostrophe ('). Both forms are considered correct. For example, you can write "Carlos's car" or "Carlos' car" to show possession. Just be consistent in your usage.