How can I add a passenger in my flight booked with Wizz Discount club? I can’t find the option.
Adding a passenger would mean you're changing your booking. It's likely that as a low-fare airline, Wizz does not permit bookings to be changed or added-to, or doesn't permit new bookings for someone (the person you want to add) who isn't a member of the Wizz Discount Club.
In other words, there may be no link because it can't be done, or can't be done without additional charges. You might contact Wizz to ask them.