Additional option of 'nodetool ring' command is not documented.
Patch has been attached.
Some history (I think it will be useful for someone who will have the same problem):
I have 4-nodes cluster. One of nodes is located in other DC (DC2). I've met the problem that 'nodetool ring' shows that node in DC2 'Owns 0.00%'. I've found following questions:
and task with fix:
So you should use 'nodetool ring keyspace' for getting right information.