You might think of it like this. The sentence could be rephrase as: Why should he notice his car out of all the other cars or things that he could have noticed.

"In particular" acts as an adverbial phrase to modify the verb "notice" and the meaning might be clearer if you place it next to that verb: "Why should Bob notice IN PARTICULAR that car. The meaning of "in particular" is "precisely and especially".

"There were lots of cars. There was a bright red Ferrari. There was a silvery Tesla Cybertruck. There was a Volkswagen minibus with rainbows painted on it. Jim's car was a plain old Toyota Corolla with nothing special about it. Why should he notice Jim's car in particular?"

In this sentence, "in particular" means especially or specifically. It emphasizes that the question is about why he should notice his car rather than other cars or anything else. Rephrased for clarity: * "Why should he especially notice his car?" * "Why should he specifically pay attention to his car?" It draws attention to the specific focus on his car, suggesting there might be something unique or important about it in this context.