Upon detecting a block that is already claimed by another inode, fsck(1M) prints the duplicate block number and its containing inode (after I=).
In fsck(1M) phases 2 and 4, you decide whether or not to clear these bad blocks. Before committing to repair with fsck(1M), you could determine which file contains this inode by passing the inode number to the ncheck(1M) command:
# ncheck -iinum filesystem
For more information, see the chapter on checking file system integrity in the System Administration Guide, Volume 1.