Hi,
When we hover over a contact in Outlook, it pops out the contact group information that the contact belongs to. Is this what you want to achieve? If this is the case, I'm afraid there is no such build-in feature in Outlook.
I'd recommend you post your question in one of the following two forums to check if this is possible via coding:
https://social.technet.microsoft.com/Forums/scriptcenter/en-US/home?forum=ITCG
https://social.msdn.microsoft.com/Forums/office/en-US/home?forum=outlookdev
The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with
us. Thank you for your understanding.
Steve Fan
TechNet Community Support