It could be 1123 or sometimes even 0124. While selecting the NOC, the duties and responsibilities mentioned in the NOC should be a close match with the actual duties and responsibilities carried out by you at the respective job. You need not match the duties and responsibilities word by word, but the idea is to have the closest match in terms of the spirit of the duties and responsibilities (at least 60%-70% match).
Also, NOC should be selected on the basis of the match of actual duties and responsibilities carried out by you rather than the designation match in the NOC list. If you are not sure of your NOC, write to
noc@workingincanada.gc.ca with your duties and responsibilities, they will help you find the closest fit.