When someone says "Jummah Mubarak" to you, it is a traditional Arabic and Islamic greeting exchanged on Fridays, which is considered a blessed day for Muslims. "Jummah" refers to Friday, and "Mubarak" means blessed or happy. To respond appropriately, you can say "Jummah Mubarak" back to the person who greeted you. It's a simple and courteous way to acknowledge the greeting and reciprocate the good wishes.
If you are not Muslim but want to respond politely, you can simply say "Thank you" or "You too" as a respectful acknowledgment of the greeting without using the specific Islamic phrase.
Remember, responding with kindness and respect is always appreciated, regardless of your religious beliefs or cultural background.