No rule for this one
No ending or word group predicts the article of Praxis. Learn it as a pair and say it out loud: die Praxis.
die Praxis
It's die Praxis. Praxis is feminine, plural die Praxen.
Die Praxis ist heute geschlossen.
The practice is closed today.
No ending or word group predicts the article of Praxis. Learn it as a pair and say it out loud: die Praxis.