I'm told that the scientist is on a different island but i cant find him,how can i find the scientist on the island?
You need to travel to Icycull.
I'll give a brief explanation:
Once you beat the Queen, talk to the Tiana then head to the Casino. Get a VIP Pass and talk to the Don. Beat him at his game 5 times in a row. Go to the harbour, head to Icycull. Cross the mountains to Icycull. Talk to the people there and the chief. Cross through the Dread Mountains. You'll be in Mezeti. Head to the tavern and watch the scenes. If you watched, head out and follow Mallory. If you intervened, go to Beth's house. Nap until its night time and you'll find the doctor outside. Follow him around and you'll end up at his lab.