Retrive on premise data

[Ayush_15]

Hi All,

My end user has windows AD which are on premise.
Those are synced to Azure but there are few specific fields which do not get synced to Azure AD.

I need to retrieve data of those fields from those ID's .
For example : 
Id Name : abc@domain.com
Desk No : 10

Here Desk no does not get synced to Azure ID and thus I am unable to fetch it .
Any leads would be appreciated.