PMI does not offer diplomas but competence based certifications such as the Project Management Professional (PMP). You can learn more about the certifications here
You can write at any Pearson Vue Test Centre in Zimbabwe. Click here, select Zimbabwe from countries drop down list then click Next to view the centres.
Go to www.pmi.org/certifications and apply for the certification that suits you. After approval by PMI, you will be eligible for the exam for the next one year. You will need to pay the applicable fees online and sit for your exam during this period.
The Chapter currently has an exam preparation group on Whatsapp. Get in touch with us to join the group.
This varies from individual to individual. Some prefer to study on their own whilst others attend exam prep classes.
You would need the most recent version of the PMBOK which is the 6thedition. A digital copy is available for download for PMI Members.