Hi Muhammad Zeeshan,
Thank you for posting your query on Microsoft Q&A!
The answer to your question would depend on who you want to see this attribute, does it need to be viewable to all users, in Teams our Outlook etc.. or is its purpose for reporting or admin use only.
You can add it to the display name, the job title, department, or you can create a custom attribute which is only visible via PowerShell.
If you let me know more about your use case I can help suggest an appropriate location.
Kind Regards, Donal