How many subunits does glucose have?

It has only one. We refer to subunits when we talk about polymers, which long molecules made up of joined monomers, rather like a necklace made of many beads. The beads are the subunits. Glucose is not a polymer, it is a monomer. Amylose, one of the constituents of starch,is made of at least a thousand glucose subunits.