Yourdictionary.com and couple of others provide this definition for "assignment":
A position or post of duty to which one is assigned.
The journalist took an assignment in China.
Is this the same as "a job"? Does the sentence mean that the journalist took a job in China?
Some other definitions state that it's:
A piece of work that has been assigned (source thefreedictionary)
Is assignment not only a piece of work but also your occupation? Something you do for a living. Can I say "My assignment for the last 20 years was a taxi driver"?
Best Answer
Yes, you can say it if you wish but it would be misleading unless someone had assigned you to be a taxi driver, which would be most unlikely.
A job is a description of any kind of work a person or organisation undertakes, whether paid or unpaid.
An assignment is of its nature usually a temporary function/commission/appointment in which somebody is sent to do a particular job for a time.
If you are for example an accountant, you can be assigned to a particular desk or account; a policeman to a particular investigation, a soldier to a particular unit, a banker to a particular branch - and so on.
In all these cases, somebody senior assigns someone more junior to do the job.
So, in your example, the journalist undertook a particular job in China to either report on or investigate or follow up a story.