A job typically refers to a specific paid position. A person, such as a doctor or teacher, has a job to earn money and sustain his life.

Example: My job at the local high school involves teaching students about foreign languages.

A job can also refer to a single task or event. This is especially true in the case of freelance work, such as photography.

Example: My job for this week is to finish analyzing our financial reports.
Example: I just got hired on a job to photograph a couple's wedding.

In contrast, work is a much more universal term. It could or could not be attached to a job.

In terms of a job, one's job involves the completion of work.

Example: As a doctor, I go to the hospital to perform emergency surgery. [doctor = job; emergency surgery = work]

Work can also be used to refer to one's place of work.

Example: I am going to work.

Work can also refer to the product of one's effort.

Example: My portfolio contains only my best work.

Lastly, work has numerous uses that are not related to a professional job. Work can be almost anything that requires effort. Here, work refers to the act of putting forth effort to accomplish or create something.

Example: Doing math is hard work.
Example: It takes a lot of work to build a house.

To summarize:
Job - is a professional position or a single task
Work - is expended energy and effort, a place where work occurs, or the product of work