By adding Tags to the questions of your Exam, you can keep scores to certain subcategories within the test.
Here you will find the instructions how to set up Tags and use them for your questions:
If you go to the "EXAMS" Tab in the dashboard of your account, you can go to "Manage Tags" in the menu:
There you will find the option to add any number of Tags.
Once you've done that, you get to select any of those Tags for every separate Question:
At the end of the Exam, when a user has answered all the question, he/she will see a general score as well as a score per Tag:
You can also review these results from the "Results & Stats" page of your exam dashboard: