Can I create subcontracting order for assembly order in Business Central?
Answer is NO for out of box BC. As mentioned subcontracting is a feature for premium license BC users in the manufacturing module. With that being said, there are people who created a workaround by setting up contractors as resources and use specific accounts to track costing for those vendor resources.
Can I create subcontracting order for assembly order in Business Central?
Assembly Orders are not meant to be used with Subcontractors, so the answer is no. An Assembly Order is a kitting process where you gather a few Items and put them in a box or bag under a different name. It is not something you would sub out.
Production Orders would be used if the work is outsourced, which would require the Premium license.