Many different types of oil are suitable for a wooden kitchen knife handle. The most accessible kinds like mineral oil, Danish oil, and linseed oil works fine. Pay attention to the amount you need to apply on the knife handle, as oils react differently. For example, you'll need to lay more mineral oil than Danish oil. Also, avoid using cooking oils such as olive or canola oil. These oils can leave you with a smelly handle as they will go rancid over time.