A great way to get started is by having them visit couple of websites/video tutorials as starting point:

1) https://www.scrumalliance.org/community/articles/2007/april/being-an-effective-product-owner

2) http://scrummethodology.com/scrum-product-owner/

Once the product owner has the basics from the above, I start them with writing simple user stories and coaching on grooming sessions. (You might have to start with initial list of stories for the backlog)

If the organization is using any of the SCRUM tools for managing the backlog, I would have him/her start them get familiar with that.

and the rest is simply having them being engaged throughout the project and they will pick it up.

I agree with above response. We have one of the presentation from Pega Consulting on "So You Want to Be a Product Owner". We used attached Pega Presentation with our client to enable and guide them thru the Product Owner role and Scrum Foundations.

I would suggest the hardest and most difficult part is making sure that the new Product Owner is empowered to make decisions in order to achieve the project's business outcomes. 

Often product owners lose euthusiasm for their new role when they have to refer everything to committee as would occur prior to the organisation taking on Scrum. 

Understand the frame work of PEGA that would best fit after knowing the domain of the project that you are going to be involved in.

Which would help you gain a lot capabilities that the product has been carrying by default

Excellent suggestions and content above.  I agree with all these postings. 

I also set the expectation with the client Product Owner on the time committment to come up to speed.  They probably started during the Sales cycle but continues with each engagement.  Ten (10) hours per week (front loaded) is a minimum. 

Pega is feature rich and it takes time to learn.