Non EU trainees having an opportunity to make a traineeship in Belgium must follow certain rules and need in principle an authorisation.This authorisation should be applied for by your employer to the competent regional government in the form of an application for authorisation to work, which will then be considered as an application for a authorisation for trainee.
For the conditions and the procedure consult the following Iinks:
GOOD TO KNOW: are allowed to do a traineeship in Belgium without any authorization (only in the framework of a training) foreign nationals who, as a student, complete obligatory trainings in Belgium, for the purposes of their studies in Belgium, in a member state of the European Economic Area or in the Swiss Confederation.
Click here to see the list of situations that are exempted to a work permit.