It is common to see a confusion between the term Publish Key and Public Key. These two terms are very different.
Publish Key is a term used in the PubNub universe which describes a key with Publish Send capabilities. The PubNub Publish Key is required to be paired with a Subscribe Key. The Publish Key is required for sending JSON messages over PubNub Data Stream Network.
Now let's talk about the purpose and context of Public Key. This term is typically used in cryptography/encryption universe and reserved as the open key. RSA offers Public/Private key generation and encrypt/decrypt methods.
i have signed up in pub nub. how can i know my public key?
Public Keys are generated via RSA and are optional. You don't need a Public Key. I recommend continuing forward from here without a Public Key until you identify the need for one.