Na laboratory experiment, john uses a mesh to separate soil particles from water. which technique of separation is he using?

He is using the filtration method.
It’s a technique which is used for separation of solids and fluids by putting them through a medium which allows only fluid to pass through, leaving the solids (in this case the soil) alone.
The fluid that passed is called the filtrate.

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.