1. What actually mokshin is? is it PC name or informix connect (setnet32) username?
The value "mokshin" is actually the userid that the program passed to the server. We see this error message all the time becuase out client application requires the user to type in their userid and password and they miss-key. If this is the case for you as well, it's usually only a random thing and nothing to worry about.
Some sites set their userid and password in the setnet32 configuration. It could be that your PC support group entered the values wrong.
2. Can I detect the location of user mokshin? such as IP number or mac address....
No. Even when a userid is logged in, the best you get is their "TTY" name - the internal name of the PC. Many folks wish that Informix actually captured and retained the IP address (since the server obviously knows it) but I've had several developers explain to me why they can't.