Query below returns tables in a database with space used by their indexes ordered from the ones using most.
select tabschema || '.' || tabname as table, index_object_p_size as index_size from sysibmadm.admintabinfo where tabschema not like 'SYS%' order by index_size desc;
- table - table's schema name and name
- index_size - space allocated for table's indexes