If you want to communicate with another user using public$-$key encryption for confidentiality, your messages need to be encrypted using the user's public key. The best way for you to get the public key of the user is to

Question $20$ options:

ask the PKI server to send it to you with a digital certificate

ask the PKI server to send its digital signature to you

ask the PKI server to send its private key to you

ask the PKI server to send both the public and private keys to you