How do you turn into super knuckles in sonic 3 and knuckles

You need to collect all Seven Chaos Emeralds. In Knuckles story it take you a little longer because your not the same route as Sonic & Tails. In order to get all seven Emeralds you need to go through Giant Rings and do a Special Stage for each one of them. Once you finished a special stage you will receive a Chaos Emerald if you lose you can try again but the same Ring won't reappear in the same spot so you need to look all over the area to find more.