Hey Niels, thanks for your idea!
gpg -K:
/home/hommesf/.gnupg/pubring.kbx
--------------------------------
sec> rsa4096 2018-09-24 [SC]
[some private key fingerprint]
Card serial no. = 0005 00004FDD
That's actually all I can find.
seahorse didn't show the others neither.
Greetings
Frank
