Sashia had watched the group catch more Pokemon before she said "Well, although it's not consider trial per say. I know of a den where another Totom Pokemon makes it home. 
It's quite close to where Tapu Koko shrine is, and it's said that he watches those who go into cave and if they complete the Totom trails, they can find the special rocks which Z-rings come from. 
But the Totom there, only comes out at night and the trails can last into the early morning. I got my Z-Ring from Kahuna Olivia of Akala Island but I know Mike had to do it to get his ring. I can take you guys there if you like but be warned, you have to work hard to prove that you can wield the Z-Ring and unleash your partners full potential. Mike told me that you have to use only your first partner in Aloha to do these tests. Mike and his partner The Hood/Rowley did the trail"