You can open the Object Inspector from the View menu. Then, after you select a variable, corresponding object is presented in the Object Inspector.
In the object inspector you can "drill down" by double-clicking an item or field. You can go back to previous object using the left arrow button in the header of the Object inspector.
(You may wonder why does Thonny have separate view for this instead of allowing investigating the structure of the object in the variables view. I simply wanted to stress the difference between variable and object. As you can see, the Object inspector labels the object by its address, not name. This is meant to illustrate that you don't need variables to speak about objects. Try evaluating and expression in the Shell while the Object Inspector is open.)
Best regards,
Aivar