How do I discover the Oracle Express workspace name?
There are two tables you can get this info from.

APEX_WORKSPACES and APEX_APPLICATIONS.

The schema that these tables reside in depends on the APEX version. By way of example, my vanilla Oracle 11.2 install has them in the APEX_030200 schema. To list: select USERNAME from DBA_USERS where USERNAME like 'APEX%'.