No rule for this one
No ending or word group predicts the article of Kurs. Learn it as a pair and say it out loud: der Kurs.
der Kurs
It's der Kurs. Kurs is masculine, plural die Kurse.
Der Deutschkurs ist gut.
The German course is good.
No ending or word group predicts the article of Kurs. Learn it as a pair and say it out loud: der Kurs.