It is on the front side of the receipt, sometimes it is mentioned as reference number sometimes it is file number
Check this out to see which tracking number you have.
https://etatpasseport-passportstatus.service.canada.ca/en/landing
I found my reference number, however, when i enter this information on the passport tracking website it says we received your application and it is under processing. This status does not update according to some posts i saw on other forums. Is there an alternate way to track?