SQL Query: From two different DataBases

SELECT *
FROM [MyDatabaseOnDB1].[dbo].[MyTable] tab1
    INNER JOIN [DB2].[MyDatabaseOnDB2].[dbo].[MyOtherTable] tab2
        ON tab1.ID = tab2.ID

The naming convention you have "DestinationServer.dbo.DestinationDB.DestinationTable" is incorrect. its ServerName.Database.dbo.Table. 

select AdmissionNumber from portal.dbo.vwStudCYCurrent