To list all user tables in a SQL Server database that have no Clustered Index defined, you can use the following query:
SELECT DB_NAME() AS Database_Name
, sc.name AS Schema_Name
, o.name AS Table_Name
FROM sys.indexes i
INNER JOIN sys.objects o ON i.object_id = o.object_id
INNER JOIN sys.schemas sc ON o.schema_id = sc.schema_id
WHERE i.index_id = 0
AND o.type = 'U'
ORDER BY o.name, i.type
The query checks for all user tables that have a row in sys.indexes with index_id value of 0. If a table has no indexes or only non-clustered indexes, it will have have a row with index_id = 0.
A table without a clustered index is called a heap.