This can be attained after completing "Location 8 - Ninjago City Downtown" (
https://www.youtube.com/playlist?list=PLnM236QQZlrNpEp1RgZqY...).
Replay the chapter with any characters and proceed until you acquire the Ancient Scroll "Master of Fortune" (2x multiplier for collected Studs).
Equip the Scroll (Hold Y and go into your character wheel) and proceed with getting a Gold Medal for all 8 Dojos which should earn you enough Studs.
The amounts needed for every rank are:
Rank 1: 50,000 Studs
Rank 10: 1,325,000 Studs
Rank 20: 4,000,000 Studs