To work out how much of your RMD is exempt from Hawaii tax, download Schedule J from the Hawaii taxation web site (make sure you get the version for the current tax year). As specified in the comments above, the fraction of your pension that comes from an employer match is exempt from Hawaii tax. Schedule J helps you work out what that fraction is.
Even if you have rolled over to a new savings scheme (e.g., from a 401k to an IRA), the earnings from that fraction of the resulting IRA retain their "employer match" identity as far as Hawaii is concerned and are exempt from Hawaii tax.
In my case, I never did file Schedule J. It was too much work and the savings in doing so were too meager to make it worthwhile. I just set the deduction to zero.
