We see the little prince's keen abilities of observation and paying attention to detail in several places. The first instance takes place when we meet the prince for the very first time. The prince opens his conversation with the pilot in the Sahara by asking the pilot to draw him a picture of a sheep. The pilot, feeling that his drawing skills had been thwarted when he was a boy drew him one of the two pictures he felt he knew how to a draw, a picture of a "boa constrictor from the outside" (Ch. 2). We learn earlier that when most people see his drawing of an elephant inside of a boa constrictor they reply, "That is a hat," which is a response the pilot uses to judge a person's abilities to reach "true understanding" (Ch. 1). However, when the prince sees the drawing he immediately replies, "No, no, no! I do not want an elephant inside of a boa constrictor" (Ch. 2). The prince's ability to recognize the picture as an elephant inside of a boa constrictor proves that he has a keen sense of perception and a keen ability to notice details. If you look very closely at the drawing in Chapter 1, you'll see that you will only be able to tell that it is a picture of an oddly shaped snake if you look all the way to the end of the drawing and notice that what appears to be the brim of a hat actually has eyes. Once you see that it has eyes, you may then be able to notice that it has a very long neck and tail, like a snake. Plus, since we know that snakes are known to swallow their prey whole, we will then be able to observe that what might be a snake is probably oddly shaped due to what it has recently swallowed. Finally, we might then be able to see that the shape inside the snake looks a bit like the silhouette of an elephant. Hence, the little prince's ability to carefully observe the picture and deduce that it is a picture of an elephant inside of a snake and that the only type of snake capable of swallowing something as large as an elephant shows us that the prince has a keen sense of perception and is able to reach "true understanding."
Other instances of the prince's keen ability to pay attention to details can be seen with relation to his descriptions of his planet and of his traveling adventures. For example, we learn in great detail why the baobab trees are a particular threat to the prince's planet. We learn that the planet is infested with baobab seeds and that if these seeds grew into trees, they would crush the tiny planet. We see the pilot's account of the prince's description of the problem with baobab seeds in the lines:
Now there were some terrible seeds on the planet that was the home of the little prince; and these were the seeds of the baobab. The soil of that planet was infested with them. A baobab is something you will never, never be able to get rid of if you attend to it too late. (Ch. 5)
Hence we see that all throughout the story the little prince is characterized as having a keen sense of perception, a keen ability to observe details, and a keen ability to reach "true understanding."