another option is you 'repeat' the calculation for work days within the Iif, ie
SELECT Resourcing.Project_Title, Resourcing.Start_Date, Resourcing.End_Date, Resourcing.[Time],
Resourcing.Trainer_Name, Resourcing.Training_Type,
dhCountWorkdaysA(Resourcing.Start_Date, Resourcing.End_Date) AS...