Thanks for your update.
When an appointment is added for multiple resources (say 2), appointment objects (2) equal to the number of resources will be created for each resource as shown in the below images. If you wish to use OwnerId parameter then for-loop (based on appointment object length) can be used to retrieve the respective owner id’s or else args.appointment.Schedule1_ownerfield_0 (for without grouping) / args.appointment.Schedule1_ownerfield_1 (for with grouping) parameter can be used.
Note: Schedule1_ownerfield_0/1 parameter will be available with all the owner id’s in all the appointment objects. It can be used to pass owner id in ajax call, since it is in sting format it needs to be split in ajax function.