Marketable skills are those that employers are seeking because they are necessary to do the entry level job. Sometimes these are related to major. For instance, most professional jobs in accounting require an accounting degree. A physical therapist must have that major and a lawyer must graduate from law school. For many jobs and careers, however, the major requirement may be more general because the skills and knowledge necessary for the job are not contained in any one major. For instance, many sales recruiters look for skills in communication, persuasion and self-direction. Many investment firms are interested in skills in research and analysis and like broadly educated individuals. Liberal arts and sciences majors wind up as successful business people, teachers, scientists and in many other rewarding careers.
For students without a technical degree, good computer skills can be the key to landing excellent entry opportunities in a variety of organizations. A command of software such as word processing, desktop publishing, spread sheets, and web development are highly sought for many jobs in almost any industry or organization.
Skills in writing for different purposes and audiences are essential in some careers and highly sought after in all but a few jobs. Business and/or technical writing skills are important for many jobs. Other writing skills sought after by different industries include informing, persuading, legal etc. Being able to organize and present information on paper is key to success in many fields. Encourage your student not to skip courses that require writing. It is best learned through practice.
There are very few jobs today that don't require the ability to work with others. Even technical or computer experts often work in teams. Students can develop teamwork and leadership skills through clubs, activities and work. More and more academic courses require group projects and the experience of working with others is as valuable as the course content learned. Working with others who are a different race, sex, religion, age etc. is an outcome increasingly being sought by recruiters. It's not unusual to see questions in an interview designed to probe a student's experiences in these key areas.
Recruiters also probe for such skills as problem solving, quantitative, and scientific as well as maturity, judgment, and self direction. Depending on the job these can be more important than the major.