residence permit no. Youth mobility visa ?

Help! I've started the process of applying for the Youth Mobility Visa for Germany. I am filling in the Application form (Antrag auf Erteilung eines nationalen Visums) but I am puzzled by one thing. They ask for a Residence permit No. and I am not sure what this is referring to? I am applying from my country of residence (Canada) Could someone guide me: Do I possess this no. ? And if so, where can I find it?

Hey! I've just started my application and was also confused by that question, what did you end up answering and how did the application work out for you? Thanks!