What is Spock's second name?

Could you please clarify what you mean by "Spock's second name"? Are you referring to the character from the Star Trek franchise, Lieutenant Commander Spock? If so, it's worth noting that in the context of that universe, Lieutenant Commander Spock's full name is Spock, and he does not traditionally have a second name or surname in the way that humans do. However, if you're asking about a specific piece of fan fiction or an alternate universe where he has been given a second name, I would need more context to provide an accurate answer. Is there anything else you can tell me about the situation or context in which you're asking this question?