This query listed tables that have no foreign keys, meaning they are not referencing any table or are not on the "many" side of FK.
Query below lists something a little different - tables that are not referencing and are not referenced by other tables. Something I called Loner Tables. This diagram illustrates the concept:
select 'No FKs >-' refs, tab.tabschema concat '.' concat tab.tabname as table, '>- no FKs' fks from syscat.tables tab left outer join syscat.tabconst const on const.tabschema = tab.tabschema and const.tabname = tab.tabname and const.type ='F' left outer join syscat.references ref on ref.reftabschema = tab.tabschema and ref.reftabname = tab.tabname where tab.type ='T' and tab.tabschema not like 'SYS%' and const.constname is null and ref.constname is null
Loner Tables in GSDB: