The reading that matches the accountability as the Scrum Guide defines it, including what the PSPO exams assess.
The Product Owner accountability is narrower than product management and more precise about what it requires. These books are ordered from the ones that define the role to the ones that develop the judgement it needs. If you are preparing for PSPO I, the first two are the closest to what the assessment covers.
Written by Scrum.org trainers and the closest book to what the PSPO assessments actually test. Precise about the accountability rather than the folklore around it.
Short, accurate, and careful to separate what the Scrum Guide requires from what teams merely tend to do. That distinction is most of the difficulty in the exam.
The reference to keep on the desk. Covers every part of the framework in enough depth that you can look up a question rather than guess.
Goes past the mechanics into what separates an ordinary Product Owner from a good one, using paired examples of the weaker and stronger behaviour.
Pichler on the role itself, including the dysfunctions such as the proxy Product Owner and the committee that are worth recognising early.
Still the clearest treatment of writing items, the INVEST criteria and splitting work that is too large to pull into a Sprint.
The Product Owner accountability is about value, and this is the book on what happens when an organisation measures output instead.
Product strategy and roadmapping in a form that connects directly to a Product Backlog rather than sitting above it.
Eighty pages on tracing every backlog item back to a goal and an actor whose behaviour must change. Useful for defending what you left out.