To be able to find you brands Google Analytics ID you need to have an active Google Analytics account to setup the "Tracking ID" to be used to integrate against your campaign landing pages within TargetEveryone.
If you do not have a Google Analytics account, learn how to setup a Google Analytics account here: https://support.google.com/analytics/answer/1008015?hl=en
Google Analytics Tracking ID is the code that let Google Analytics recognize the source (this would be your campaign landing page in this case) to extract all valuable insights about your target audience behavior and demographic details.
Learn how to setup a Google Analytics Tracking ID: https://support.google.com/analytics/answer/1042508
This is where to find your "Google Analytics Tracking ID` within Google Analytics interface:
1.Go to Admin:
2.Click on the "Property Settings" option
3.And now you will see your "Google Analytics Tracking ID"
If you wonder why it is a good idea to implement this? Read this
What kinds of statistics and graphs you can access by implementing GA ID on your TargetEveryone campaigns, you find here