Switch Partition is not appearing under configure of a Sub-Object Based Portlet.
This was available in previous versions on PPM/Clarity.
The ability to switch partitions on a sub-object portlet was removed. The reason that it was removed for sub-object portlets is because subobjects inherit the partition unit of it's parent instance. All views for subobjects are expected to appear for one partition unit which is the inherited unit of it's parent instance.
Switch partitions option is available on master object portlets only.