In Service Studio you can use web screens that are exposed by another eSpace, called, in this context, a Producer. Simply add these web screens as eSpace reference of your eSpace, called, in this context, a Consumer eSpace.
How to Add a Web Screen Reference:
Once web screens are added as references, you can use them in your eSpace:
In any element property where a web screen can be set, such as, for example, the Destination property of a Link element.
How Web Screens are Handled
Once a web screen is added as a reference in the Consumer eSpace, you can use it like any web screen originally created in your eSpace. However, you cannot change the design of the web screen.
Add/Remove eSpace References | Expose a Web Screen | About Platform Server Session