Getting a key size of DSA/Elgamal certificate I've tried to get a public key size of DSA/Elgamal PGP certificate. Using the Cleopatra I find out that there is actually two public keys - one with DSA with key size 1024 bits and the other Elgamal with 2048 bits. 
Now my question is which of this key sizes is the actual key size for this certificate and more importantly, why?
It's extremely likely that 1024 is the master key size as authentication and signing are usually the main purposes of PGP. The key used for encryption is generally valid for a shorter time and is therefore a subkey of the master key. So both 1024 and 2048 bit public keys are included in the PGP certificate.

Note that the key size for encoding the key will be larger and the key strength (compared to e.g. an AES key) will be much less.

Both 1024 and 2048 bit keys are rather small for common purposes. It is highly advisable to upgrade to larger, RSA based keys. For more information about key sizes and their strengths, please take a look at https://keylength.com.