List all used data types of a table or whole database in Oracle DB
Here is an example to find the number and type of columns in a schema:

select data_type, count(*) from dba_tab_cols
where owner = '...' group by data_type order by data_type

DATA_TYPE              COUNT(*)
-------------------- ----------
ANYDATA                       6
BLOB                         32
CHAR                      12335
CLOB                        259
DATE                      16923
LONG                          2
NUMBER                    39618
NVARCHAR2                     9
RAW                          53
ROWID                       270
TIMESTAMP(3)                 37
TIMESTAMP(6)                109
VARCHAR2                 132291
XMLTYPE                       2