You need 100 mojo to get one reward from the gift machine. You get mojo from playing songs (5 per star ranking), leveling up and completing daily challenges
You also get mojo from various rewards available on the Ubisoft Club (700 total) and even more when activating your free trial of Just Dance Unlimited (it won't renew automatically after the trial period is over).
Finally, if you have the game on multiple platforms, you can get more mojo from the Ubisoft Club by redeeming the rewards for each platform. The mojo will be added to the save linked to your Ubisoft account which is synced across platforms.