Let me make an attempt to explain the process that needs to be followed in identifying KRAs based on a basic JD.
1. List your main day-to-day responsibilities/activities (JD).
2. For each activity, ask "Why do I do this?"
3. Review the answers to your "why" questions, looking for common areas.
4. Identify your KRAs from these areas.
5. Share your KRAs with those you report to. Needless to say, KRAs should be SMART - specific, measurable, achievable, realistic, and time-bound.
Key Result Areas usually capture 80% of a work role, and the remaining 20% of the role is devoted to shared responsibilities, which may include process improvement and subordinate development. Most roles should include at least 3 KRAs, and the maximum range could be 3-7.
Please let me know if you need any further assistance or clarification.