Is it possible to fetch user event data using Graph API for personal premium Microsoft accounts
you mention its a personal premium account, then you say user is present in azure ad.. there are a few conflicting statements here, if you could clarify, 
there are no such thing as a personal premium account. Microsoft 365 is either business premium, personal or family. there is no personal premium.. 
If it is a personal office 365 account, then it does not have Azure ad. and you can only grab limited data for that user through graph, by using the /me endpoint. i would highly doubt that you could access a personal account's calendar.
if you are talking about a business premium account, then that comes with azure ad, and you should be able to interact with the users through graph as per documentation. but you would still need to grant more permissions for calendar for example to read someone elses calendar. 
If it is a personal o365 account that you added to a different o365 business tenant, that user still does not belong to your tenant, because at its base its still a personal account with no real azure ad tenant. 
hopefully that clarifies a bit.
We are trying to fetch event and calendar information for user through Graph API. User is present on Azure Active directory and has active o365 subscription. /events or /calendar APIs  are not working. Is it possible to do so through non work premium Microsoft accounts?