If the coworkers in your dream are not your actual coworkers, then they may symbolize an aspect of your personality that you need to alter or improve.
To dream that you are training someone to take your place implies that you are ready to begin new projects and encourage personal talents and abilities to grow. You have adopted new perspectives to replace previous ones. *Refer to Office. [1]
Your work or workplace.
Teamwork, or your typical dynamics with that person (such as cooperation, competition, or animosity).
A coworker from a past job could represent that person, that job, or that time period in your life.
See also: Person You Know, Workplace, Manager, Working, Time Frame, Past [2]