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.
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.