what to do if PO is not doing his job?

Ownership of the process should belong to the Scrum Team and no-one else. This means that a team should be able to remove its own impediments, and should not need to escalate them to anyone else for resolution. Coaching, and inspection and adaptation through retrospectives, are good ways to achieve this.

Thanks Ian. that helps alots

ironically I also got 82.5% , and every time I've done the open assessment I've had the Scrum Master is a management role question marked wrong in a Utopian world maybe, but when you have to implement scrum from the ground up and then bit by bit get the pieces of the framework in place, which includes labouring to have a PO role appointed for your Scrum team, what is the reality that the divisional manager will simply just leave this in the teams hands to deal with ? Scrum is hard, but worth it ... but that said , not all scrum masters are appointed into roles where the framework is correctly in place to begin with. When fundamental steps have been missed in the implementation of scrum, and the dev team already feel like they have just had a new way of working imposed on them, these are real issues that scrum masters sometimes face, and I really feel that this exam shouldn't be aimed at such a wide variety of these ... some of these questions are related to enterprise level projects , with teams working with independent project portions that require integration phases.

In Scrum management is a collaborative responsibility and not a role. It's quite valid to talk about "management" and "managing" in the context of a self-organizing team. In effect, every team member occupies a management position in some capacity.

As a very general rule, if you encounter the term "manager" (implying a role), or see reference being made to management as a role, you should be a bit suspicious.

Well, I agree with most of the facts that have been pointed out by these members regarding the roles/responsibilities of the Scrum Team in this situation. However, I would like to point out that as much as it is a collective responsibility in Scrum Team, it is also clear that each component of the Scrum Team must play its role to support the frame work. By this, I mean the PO, SM, or the Development team each must play its part for the Scrum framework to make sense. Therefore, in this situation, SM should couch the PO on the importance of the Scrum team working together to support the framework.