This article explains how to display data in a GridView from two different SharePoint lists.
IntroductionThis article explains how to display data in a GridView from two different SharePoint lists from the same or a different site collection having or not having a lookup column using LINQ.Or An inner join of two SharePoint Lists using LINQ.This can also be done using a SPQuery join, provided lists are from the same site collection and properly bound with a lookup column. But if lists are from a different site collection and they do not have any lookup column then the following will definitely work.Step-by-step Implementation
SharePoint Online And Office 365 Administration