Keep in mind that where on your site you place your cookie notification matters as well. If you place it on a master page the cookie notification will appear on all pages that have that master applied. If you place it on a specific page, like the homepage, it will only appear on that one page.
If you want the cookie notification to appear only once for the user, regardless of what page they enter from, that functionality is currently not available in Brandcast. You will need to use a 3rd party cookie notification company instead, and embed that into your Brandcast site.
More GDPR resources
The GDPR is meant to protect users data. Brandcast does not collect any data from users visiting your site, and can do little to help make your site GDPR compliant. You can create a notification to alert users of cookies being used. Visit the following sites to gain a better understanding of what GDPR means for you.