'Your' is second person possessive adjective in a sentence.
it depends what word it is it could be any part of speech depending on the sentence
it is an English speech
What "part of speech" is the word "said?"
The term for knowing a word's part of speech in order to appropriately use it in a sentence is "word-usage."
The individual word "sentence" is a common noun. However, a sentence itself is comprised of many different parts of speech.
The action in a sentence is the part of speech known as a verb.
There are no sentences that have no parts of speech. Every word in a sentence is classified as a part of speech, such as nouns, verbs, adjectives, etc.
By use of the word in a sentence.
The word 'in' would be a preposition in the example sentence you gave.
The use of the word in the sentence derminates the part of speech
The word 'this" in the sentence is an adjective describing book.
It is a verb.