How do I know that I can get a job with a particular major?

There is no single source for answering this question. Even the current job market may not be indicative of what jobs will exist and be available when you graduate. To get some feeling for this, talk to the career planning and placement office at a university. The professional staff in this office can direct you to current job projections. Talk to faculty and, especially, students in that major. Students are often aware of whether recent graduates are looking for jobs and finding them or whether the job market is tough. Finally, talk to people, especially human resources people, in the kinds of companies that employ these majors to see how they see the future hiring prospects for entry level graduates.