As someone who has studied french for many years, I say "Coo-pon." Since the root comes from the french word couper (to cut).
I actually say it both ways.

I can say all the words properly if I think about it but if I am just talking they come out like that.My husband's grandmother says it "Q-pen" YES-- PEN
I had to show DH this poll! He always laughs when I say coopon (he's the q pon type)
how about "coo-pin" like that comedian Tator Salad, lol. This is a fun word at my house!
That is why i started it! I say Coooooopon and df makes fun of me, he claims Qpon is correct. BTW "cooooopon" is in the lead.