Get Total in a single line in SQL Server
You need to modify the GROUP BY and the ORDER BY clauses.

Try this:

SELECT 
       ISNULL([Task IT Assets], [Project IT Asset]) AS Asset ,
       SUM(P.ActualWork) AS taskHours
 FROM
      IR.TimesheetHoursProjectTask p 
 WHERE
      p.ActualWork &gt; 0 AND 
      ([Task IT Assets] IS NOT NULL OR [Project IT Asset] IS NOT NULL) 
 GROUP BY 
      ISNULL([Task IT Assets], [Project IT Asset]) 
 ORDER BY
      SUM(P.ActualWork) DESC 


As an aside, note that your table is literally named "IR.TimesheetHoursProjectTask" and not "TimesheetHoursProjectTask" under the "IR" schema. To specify the later, using the [] notation, it would be [IR].[TimesheetHoursProjectTask].