Just drop the union, and bracket your select statements:
select
(select sum(Recp_Qty - Issd_Qty)
from Reciepts where JobNo != 'stk'
group by IT_Name) as AJob_av,
(select sum(Recp_Qty - Issd_Qty)
from Reciepts where JobNo = 'stk'
group by IT_Name) as AStk_av