Incomplete question. I inferred you meant knowing which word (s) in the sentence has a preposition.
Explanation:
Remember, a preposition is a word or group of words used in a sentence to show time, place, or location/position. It is usually placed before a noun, pronoun, or noun phrase. For example, words like "in," "on," "of," and "to," "last," are commonly used.
The preposition in the sentence is underlined and bolded, where there is no preposition (#NA ) is written: