I'm having a bit of trouble helping you with these questions because of the way that they are worded, but I'll try.

"What are the physical and chemical properties used/tested in this lab."

I'll assume you are referring to an experiment in which you are trying to extract Casein from milk.  Tested in this type of experiment would be solubility (in this case, the ability of a solid, Casein, to dissolve into a liquid), protein denaturation (making a protein lose its structure) and the concept of polymers (long chains of molecules strung together.)

I'm not really sure what the second question is asking, the part about the "percentage protein recovered in milk."  It sounds like it's a question about the amount of protein in different kinds of milk based on milk-fat. The fattier the milk the more Casein you can get out of it, so I suppose you could collect data about the quantity of Casein removed from different samples as a way to compare the original protein in the milk.

The third question is most straight forward.  Depending on the type of cow, milk is usually made up of a pretty similar composition: water, protein, fat, lactose, and ash.  If you let milk sit, the fat rises to the top because it is lighter.  All of the fat is skimmed off, and then depending on the type of milk you're trying to make, some is put back in.  At the milk processing plant, this is actually accomplished by using a centrifuge.  It spins the milk around, forcing the separation.