To limit as much as possible that end users open Tickets for questions/problems whose answers/solutions are already present in the Knowledge Base, in the Service Operations (Tickets) there is a standard Knowledge Base field.
This field, through a select, will propose the articles related to the scope of the ticket that is being created, if any.
The articles and the Knowledge Base to which they belong, to be proposed, must be visible by the current user and in the area in which it is located (User Portal or Guest Portal).