Use the Query Assemblies+ v1.2 component to find all the existing Assemblies in the project.
In Revit API, Worksets are represented by the DB.AssemblyInstance.
Finding Specific Assembly
To find a Assembly by name use the Query Assemblies+ v1.2 component.
Reading Assembly Elements
Get or Set Assembly Elements using the Assembly Members+ v1.2 component.
Creating an Assembly
Create a new Assembly Type with the Assemble Elements+ v1.2 component.
Adding Assembly to Project
Add an Assembly Type to a Project Location with the Add Assembly+ v1.2 component.
Disassemble Assembly instance with the Disassemble Assembly+ v1.2 component.
Get and Set the Assembly Origin with the Assembly Origin+ v1.9 component.