Your rule key will have a very specific pattern, without spaces. You can see it when you browse the rule in SonarQube. You probably defined it yourself when you developed the rule!
So in this examle, the rule key pattern is the rule key itself, cpp:S3805. If you want to have this rule only apply on rules in ariel1/src/poc, you should define ariel1/src/poc/**/* as the file path pattern.