How does Peppol know where to route my invoice?

Via the recipient's unique Peppol ID.

Every organization has a unique Peppol ID, usually based on its company number (in Belgium 0208:xxxxxxxxxx). This ensures every invoice automatically reaches the correct company. For Belgian company numbers, the prefix 0208 is used, followed by the full company number. The company number always starts with a 0 or a 1. For example: 0208:0xxxxxxxxx or 0208:1xxxxxxxxx.