As per the Scrum Guide “The Product Owner is responsible for maximizing the value of the product resulting from work of the Development Team”. To MEET this, the product owner has to have mastery in many areas but only a few can be termed as critical because that is something which is a ‘must-have’ for this role. First, the product owner should have the ‘Business Analyst’ skill for concisely and correctly defining requirements but also have the domain knowledge and business knowledge to be a decision-maker to determine and prioritize what those requirements should be. Domain knowledge is the core subject for any product owner to master in their area and also KNOW the market and how the workflows are one of the critical skills required. 

Second, “PROJECT Management” skills to make good risk-based decisions on managing the project to make it successful from an overall business perspective (not simply MEETING defined requirements). The person opting for the product owner role has to strike a balance between these two provides the team with the OPTIMUM work.