Fungi of Si'ned VIIįast travel to the Fungi of Si'ned VII in The Itching Fields. Slap the cube off the cliff to area below. Look down again to see the green cube on another cliff below. You won't likely see the cliff before you jump, but be ready to move backward once you start falling to catch it. Go off the side of the mountain and land on a small cliff below. You will pass through the herd(?) of Pufferbird and a few roaming Jellywaft. Go diagonal and right toward the edge of the cliff. Below are the areas and biomes in which you can find them. There are three osmotic green cubes in Savage Planet. Do this a few times (three to four) and the green cube will explode, giving you the resources it consumed as well as any Alien Alloy. Just slap it toward the resources dropped by the fauna, and it will gobble them up. The green cube will sometimes try to slowly crawl back to where you originally found it. Once you kill the fauna around the green blob, it will eat the carbon and silicone the fauna drops. It doesn't matter what type, though killing Pufferbird is obviously easier than killing Kapyena. Slap the green cube to a location with a bunch of fauna.
How do you kill/open/blow up a green osmotic cube in Journey to the Savage Planet? By making it eat too much.
After several hours of trial and error - shooting it with my pistol, ground-pounding it, slapping it off cliffs, and peppering it with bombegranates - I finally figured it out.