Not sure how to manage tags for your Knowledge Model?
Then click on the "Tags" on the top of the Knowledge Model page.
You can manage the tags now. Check what tags you want to be connected with which questions from your Knowledge Model.
To finish managing the tags, don't forget to click on the "Save button".
Note that you can manage the tags for each question also in the Knowledge Model Editor by ticking the chosen tag(s) for that particular question.