Is the cum (fluid) seen in porn real or fake?

Both is possible. If you see it at most convenient times and places, or if you see a lot of it, then it is fake of course.

Years ago, I heard a poscast with a female porn director (Ovidie, if memory serves), where she gave a recipe for fake cum, based on egg whites and condensed milk.

I read somewhere that sometimes a saline solution is used to make the load look huge