What does solubility limit mean in practical terms?
Q1) If 20 micrograms / ml is the upper solubility limit and you added less than 20 micrograms the solution could be less concentrated but a concentration higher than 20 micrograms / ml H2O can't be achieved.

Q2) No more than 20 micrograms of glycerol monolaurate will dissolve in 1 ml of water so if more than 20 micrograms was added the remaining undissolved powder would stay separated in some way (eg. precipitate) which could be filtered (as @MaxW has stated), or a colloidal suspension could also form. If more than 20 micrograms / ml were to be used the supernatant (GML/H2O layer) could be estimated to be 20 micrograms/ml) after filtration.