Walkthrough: After defeating Molayne and proving that you are indeed ready for your next Trial, you will gain access to the Observatory on Mount Hokulani. This is where your next Island Trial can be found, the one set by Captain Sophocles. When you find Sophocles in the back, he will tell how he has created a system to summon the Totem Pokemon, but it ends up causes the power to cut out. You must then answer audio questions to fix it, resulting in you battling a Level 27 Grubbin and two Level 27 Charjabuug as you answer correctly.
After correctly answering all three questions, you will face the Totem Pokemon, a Level 29 Vikavolt. Unlike previous Totem Pokemon, all of its Stats will actually be boosted once the Battle begins, and it will be able to call upon Level 27 Charjabug to assist it in battling your trainer.
After defeating the Totem Pokemon and all the Charjabug it calls on for help, your fifth Island Trial will be complete. Sophocles will give you Electirium Z, as Molayne joins the two of you. Molayne himself will give you Steelium Z, the Z-Crystal apart of his former Island Trial, as well as giving you the Professor's Mask in hopes of you returning it for him. (Yes, Professor Kukui is actually Masked Royal. This will hinted throughout your journey, and shown at the end of the Main Storyline.)