Unless someone removed the ratchet dog from your loom, it isn't missing—it's hiding. The ratchet dog on the Wolf looms and Standard Floor Loom can be flipped up, and then it can get caught under shafts 1 and 2. When this happens, these shafts will sit higher than the other shafts on the loom.
With one hand, lift shafts 1 and 2 as high as they will go; with the other hand, flip the ratchet dog down onto the ratchet gear. Now all the shafts will sit at the same height, and the ratchet dog will engage with the ratchet gear.