Events pick/select instances.
When your mouse - Left button clicked occurs, it selects/pick the clicked instance in the SOL (selected object list).
From there, an action on the object type (in your case obj_test) will have effect only on the picked instances of that object type.
In this case, the single obj_test instance clicked is the one you will use as reference.
So your action go to layout (by name) is obj_test.target
This will automaticly go to the layout which names is stored in the clicked instance of obj_test.
I hope it answers your question.