You need to query the data dictionary, specifically the USER_CONS_COLUMNS view to see the table columns and corresponding constraints:
SELECT *
FROM user_cons_columns
WHERE table_name = '<your table name>';
FYI, unless you specifically created your table with a lower case name (using double quotes) then the table name will be defaulted to upper case so ensure it is so in your query.
If you then wish to see more information about the constraint itself query the USER_CONSTRAINTS view:
SELECT *
FROM user_constraints
WHERE table_name = '<your table name>'
AND constraint_name = '<your constraint name>';
If the table is held in a schema that is not your default schema then you might need to replace the views with:
all_cons_columns
and
all_constraints
adding to the where clause:
AND owner = '<schema owner of the table>'