You need to replace X with the category name. For e.g. if your category is Travel, then the variable becomes %CATEGORY_SCORE_Travel%. Please make sure that the case(uppercase or lowercase) of the category must match with the template variable.
You can add the output using Results page tab of the quiz. Please let me know if you are still confused, I will make a video on how you can setup whole quiz using qsm.
I made a video for you so that you can understand the working of %CATEGORY_SCORE_Travel%. First I ticked the correct answer. Then, I added category “Travel” using advanced question settings. And then I used %CATEGORY_SCORE_X% variable on the results page and on the email template.