Well first off how big is the tank? But I agree with others, I wouldn't introduce them, but if you really want to, I would put egg crate to separate them so they don't hurt eachother, but can still see eachother, then from there I would put a hole in it big enough for the clown knife, but not big enough for the giant gourami so the clown knife can get to cover should the giant gourami go after it. I have found giant gouramis to have mixed personalities, I've heard of ones killing large cichlids, and I've heard of ones that are very peaceful, I only kept one once and he was a gentle giant, got him at 18 inches, he grew to 26 inches before he died.