You should have been given a number once you've passed the interview and test, normally they communicate to you via email what your placement is if you passed both of these. If you are asking how to find out what number the local Union has called up most recently you should call them to find out. If your not sure of your number be sure to scower through your email before reach out to ask what it is, just looks bad if you had the email sent to you but looked over it. Hope this helps!