Open Kleopatra
Click the certificate or key you want to inspect
Right-click it and choose Details
Check the key information shown there
If you mean the private/secret key, look for the entry labeled Secret Key or Private Key
If no secret key is listed, it is not available in Kleopatra
To use or export it, make sure you are viewing the correct certificate pair
If needed, open the Certificate Manager and look under your personal certificates
If the key is missing, import the backup of your secret key into Kleopatra