You can retrieve it directly from S-Net Mobile & Desktop by clicking in your Financial situation on the “Information” button from your card. If your card is blocked following multiple wrong entries of your PIN code, it will be automatically unblocked after consulting your PIN in S-Net.

Or 

You can request a reissue by contacting Spuerkeess Direct on (+352) 4015-1. You will receive your new PIN at your home address in a sealed envelope. You can then easily change your PIN at any Spuerkeess S-Bank ATM.