If you install my component com_tc_comments, the ip address will get recorded in the jos_k2_comments table.
However, you won't get to see the IP address unless the comment gets reported as inappropriate or spam, or you look at jos_k2_comments with a mysql client.
I would like to see a change to K2 to record IP addresses, and add the IP address as a column on the K2 comments page in the administration area. I don't want to patch K2 any more than I have already with my component.