No rule for this one
No ending or word group predicts the article of Schnupfen. Learn it as a pair and say it out loud: der Schnupfen.
der Schnupfen
It's der Schnupfen. Schnupfen is masculine.
Ich habe Schnupfen.
I have a runny nose.
No ending or word group predicts the article of Schnupfen. Learn it as a pair and say it out loud: der Schnupfen.