"I will be in the IOM soon where is the best place to start researching my ancestors , the Corkhills ? "

There are a number of Corkhill lines on IOM--spelled a number of different ways. If you haven't started researching your specific ancestors, I would suggest you get a head start before you go to Isle of Man.
Starting with yourself, go backwards in time to those you know--hopefully to IOM. You probably have more IOM lines than Corkhill.
If you post an outline of your info, there are folks on this genealogy board who can probably help you.
There is a lot of info available on line as well.

If you get more specific info ahead of time, you can better use your time at the Manx Museum and in touring the specific places where your ancestors resided.

Donna