How can you infer a characters motivation

By their actions, thoughts, etc. It depends entirely on the exposition and what point of view the author provides a reader. It’s much easier when it’s a first person point of view because you’re able to directly read a character’s thought process. A character’s motivation can be family, money, romantic love, safety, just whatever drives them to continue on. I hope this helps, if you have more questions or need a more direct answer then just reply or message!