Answer:
You should look for moments when characters express a liking or disliking towards a specific person, concept, or idea in general. For example, in the book 'The Cay' we can infer about Phillip that he has a prejudice against people of color because he states multiple times the color of Timothy's skin and not being comfortable around him, emphasizing his dislike of colored people.
You can also look for more obvious moments, like when a character states themselves their opinions on a belief, though this isn't as common as you being able to infer the answer using the text
Hope this helps, and ask any questions if I wasn't clear!! <33