This article aims to describe the methodology for the design, validation, reliability, and pilot testing of a questionnaire aimed at exploring the knowledge and training needs on health inequalities of occupational health nurses (OHNs) and occupational health nursing students in Spain. Working and employment conditions are social determinants that influence the health of workers. The unequal distribution of these factors leads to inequalities. The training and competencies of OHNs need to focus on the social determinants of health to reduce social inequalities. The questionnaire was structured in five sections and 24 closed questions, self-administered and online. It was validated by a panel of experts using Moriyama's criteria and achieved an average consensus of 93.85%. Internal reliability reached a Cronbach's alpha coefficient of 0.843 and a McDonald's omega of 0.953. Participation in the pilot test was 92.5% of the sample recruited. Achieving higher levels of health of the working population requires a consensus among different social actors to integrate social determinants, gender and equity perspectives into the overall health policy of the company.