You have to query the data dictionary, specially the USER_CONS_COLUMNS view to see the table columns and the corresponding constraints like this:
WHERE table_name = '<your table name>';
Unless you are creating the table with the lower case name (by using double quotes) then the table name must be defaulted to upper case hence ensure it is so in the query.
But, if you wish to see more information about the constraint itself query the USER_CONSTRAINTS view like this:
WHERE table_name = '<your table name>'
AND constraint_name = '<your constraint name>';
But, if the table is held in the schema that is not your default schema then you might need to replace the views with:
adding to the where clause:
AND owner = '<schema owner of the table>'
If you wish to learn more about tables in SQL then visit this blog on SQL Table.