It is mentioned in the prerequisites:
"Ensure that the target XenServer opens Citrix XenServer Management API."
ref. to: https://docs.microfocus.com/UCMDB/10.32/cp-docs/docs/eng/doc_lib/Content/Citrix_Discover_Topology.htm
Question1: Is this API opened in each individual XenServer? Or is this opened in the XenCenter which manages all XenServers?
Question2: Are there any specific permissions that the API user must have? There are no permissions mentioned in the respective discovery jobs (Citrix Xen Connection & Citrix Xen Topology), as is usually the case with other types of jobs.
ref. to page 163: https://docs.microfocus.com/UCMDB/10.32/cp-docs/docs/eng/pdfs/Permissions.pdf
Answer2: There is not any specific permissions required. The job only requires permission to read Host(including PBD, PIF, CPU, VMs etc.), VMAppliance, SR, Network etc.