I think that the command getrg will show you that info.  That command will actually give you the free space left in the RG in blocks.   now you need to convert it to MB/GB/TB.  not sure what the size value of a block is...
Hello All,  Is there a way to find the size of a Raidgroup (usable by the host in GB or MB) using naviseccli commands.  Thnakyou for your information in advance  Regards Sarath 
Find size available in RaidGroup using naviseccli commands