I think we have enough pictures here to make a reasonably confident identification of the animal whose head adorns the end of the hilt of the mystery knife. I believe it is a proboscis monkey (Nasalis navatus)
which is an old world, tree dwelling monkey that coexists with the orangutan in Borneo. A wikipedia entry appears here
The male of this species grows a particularly bulbous nose, unique among non-human primates, that is thought to attract a female mate. This gives the animal a human-like facial appearance, and indeed the Indonesians use the name monyet belanda
("Dutch monkey") or orang belanda
("Dutchman") to describe the similarity in appearance to the Dutch because each had such a large nose!
If we look at the two close-up views of the knife's pommel, (Figures 1 and 2) attached here, Figure 1 shows many of this monkey's features in detail--the carving is actually clearly done in representing this animal. In Figure 1 we see the bulbous nose (A) with a clear demarkation from the upper lip (B), a clear engraving of an ear pinna set well back on the skull(C), and a flat top to the cranium. The shape on the pinna is typical of humans and other primates.
Figure 2 shows the pommel from the front and emphasizes how separate the nose bulb is from upper lip, with a clearly carved groove (A), widely spaced eyes with a clear angle between the brow and the nose (B), and again the engraved outline of the ear pinna on the other side.
Compare these features with two pictures (attached) of proboscis monkeys. The similarities are quite striking, even down to the flat top of the cranium.
The animal depicted is clearly not a dog, although there is some superficial resemblance as Detlef noted.
Given the origin of this species of monkey, I would suggest that the knife originates from Borneo, somewhere within the distribution of the proboscis monkey.