Arguably you should approach the © owner, and give due acknowledgement in any outputs you create based on your results. But I am puzzled by your assertion that the questionnaire is copyright but you don't know who the owner is. Surely there is a reference somewhere to who created it?

Safest generally to request permission, from copyright owner, when you have such wonderings—provided you are willing to not use another's content. Permission is usually safer than risking your own fair use analysis. Assuming everything is under USA law. Also assumes the items you want to use are original with the copyright claimant of that questionnaire, rather than originally from another source, such as a few items from MMPI. Daniel Kegan, Chicago.