Washington State is my residence, however, I am serving as a full-time volunteer in another state and living there during my volunteer service. Do I still claim Washington State as my State of Residence?
WA has no state income tax. You say you are doing volunteer work--do you mean you are not being paid at all? If you have no income in the state (what state?) you are volunteering in, then you do not need to file a state return there either. Provide some more information--why are you worried about what state to say you live in? If you just need to know what to put on your federal return for your address--use the address where you want to receive mail from the IRS.
Have you had any income during 2019?
DO I NEED TO FILE A TAX RETURN?
I am a church missionary and live in the State of Hawaii. I pay for all my expenses here but I plan to return to my permanent home of record in Washington State. I am just asking the question about how long I have lived in the State for the year of 2019. I assume it is all year, since I don't plan to change my home of record and I rent here in Hawaii.
Then you say you have lived in Hawaii for the year of 2019. The question still--what income are you even entering on any tax return if you are a volunteer? What are you trying to put on a tax return?