SELECT DISTINCT CLOB_COLUMN FROM TABLE;

add TO_CHAR after distinct keyword to convert CLOB to CHAR

SELECT DISTINCT TO_CHAR(CLOB_FIELD) from table1;   //This will return distinct values in CLOB_FIELD

You could compare the hashes of the CLOB to determine if they are different:

SELECT your_clob
  FROM your_table
 WHERE ROWID IN (SELECT MIN(ROWID) 
                   FROM your_table
                  GROUP BY dbms_crypto.HASH(your_clob, dbms_crypto.HASH_SH1))

---

Edit:

The HASH function doesn't guarantee that there will be no collision. By design however, it is really unlikely that you will get any collision. Still, if the collision risk (<2^80?) is not acceptable, you could improve the query by comparing (with dbms_lob.compare) the subset of rows that have the same hashes.

If it is acceptable to truncate your field to 32767 characters this works:

select distinct dbms_lob.substr(FIELD_CLOB,32767) from Table1

Use this approach. In table profile column content is NCLOB. I added the where clause to reduce the time it takes to run which is high,

with
  r as (select rownum i, content from profile where package = 'intl'),
  s as (select distinct (select min(i) from r where dbms_lob.compare(r.content, t.content) = 0) min_i from profile t where t.package = 'intl')
select (select content from r where r.i = s.min_i) content from s
;

It is not about to win any prizes for efficiency but should work.