Is it possible to trace who WMap'ed my server? How do I do so?
Assuming you are talking about this wmap tool: Well, you will have an IP address for the requests coming from the scan in your server logs and it's possible to identify the provider for the address. But since scanning your system is normally not illegal, you will have a hard time to convince the ISP (or more likely: a judge in some remote country) to identify the particular user. In short: Not likely.
I wouldn't worry about it too much anyway. As long as you don't think you are specifically targeted for some reason, being scanned for vulnerabilities is just a common situation, you "just" have to make sure your system is patched and configured securely.