Dear xavier,
really difficult to answer this "global" questions...
The corporate jet area ranges from Citations 500 to Global Expresses and the beautys from Mr.D...
Therefore qualifications asked range from 0 to a lot.
Generally speaking, a new guy is asked to have a typerating (or to buy it) and to be cheap...
These days, as the business is going slow, it is hard to get a job anyhow, very often it is a matter of luck and of personal contacts...
good luck