Hi,
you can use macro: {%Document.DocumentPageTemplate.PageTemplateCategory.CategoryDisplayName|(identity)GlobalAdministrator%}
or code behind
var template =
PageTemplateInfoProvider.GetPageTemplateInfo(DocumentContext.CurrentDocument.DocumentPageTemplateID);
var category= PageTemplateCategoryInfoProvider.GetPageTemplateCategoryInfo(template.CategoryID);
category.CategoryName
Please try it out. I didn't test it... :)