FlowJo version 11 uses a new file format, the workbench, with a file extension of .flowjo. The long term plan is to support opening both .wsp files created in version 10 and .jo files created in version 9, but that support has not been implemented thus far.
Export as a FlowJo version 10 workspace is included under the file menu as shown in figure 1.
Figure 1 Export to .wsp
This feature will produce a new .wsp file while maintaining the workbench. The output will include a flattened group hierarchy (as version 10 does not support hierarchical groups), all groups, and gates. It does not include the tables, charts, or reports included in v11.