Hi,
I would like to build KPIs based on Initiatives (Issue) and their level of completion and/or their Planning (in this case based on dates). Can you recommend some?
Thank you
Hi @Stefano89
Welcome to the Community! 
If you are using Jira Plans (formerly Advanced roadmaps) on Jira Cloud, you should first define the Initiative hierarchy: Plans custom fields
Be sure also to import the start and end dates necessary for the reports: Plans custom fields
For the KPIs, you can look at how many stories are completed from the total number of stories within an initiative, the target and the actual end dates of initiatives, cycle times of stories, etc.
You can check out our Demo account for sample reports: Start simple - Jira Demo - eazyBI
Let me know if you have any additional questions on this!
Best regards,
Nauris