Driven by curiosity and the need to know, some people just have a thirst for knowledge. From a story standpoint, while the character may start out pursuing knowledge in the general sense, their search will likely be narrowed down to a specific area at some point during their journey. This focused motivation will let the reader know exactly what the character's after and if they're successful.

There are five basic human needs that, when missing from a character's life, could motivate them to pursue this goal. The following needs are all possibilities, but only one of them should be the primary driver for any given character. For more information on the relationship between human needs and outer motivations, please see this Character Motivation tutorial.

Self-Actualization: This is the most common motivation for pursuing knowledge—the sense of fulfillment that comes from knowing more. If this is the kind of person your character is, it will be the driving force behind their desire to learn.
Esteem and Recognition: Some characters are driven by the need to be more respected by others. A character who lacks esteem may seek to gain it by attaining knowledge that others don't have.
Love and Belonging: A religious character may be driven to learn and know more about a higher power if they seek connectedness to that being.