How do I keep Clam juice
I would suggest to reduce the juice as much es possible (to safe space later on in the freezer or shelf) and either


freeze it or
can it (see here and here for canning with a pressure cooker and here for canning with an oven)


Just putting the juice into the fridge is not sufficient. Neither just boiling the juice and filling it into a jar is sufficient because then you are not sterilizing the juice but only pasteurizing.