well, for lashing, i'd want the knife (pointy thing) to be inline with the shaft...
so if you put your pint thing in line with your shaft, how does it stay? you could use thinner sticks, say at leat 3, perhaps 5 or 7 "wrapped" around both the full handle of the pointy thing and a substantial portion of the shaft (spear) with slight notches in the shaft to secure best as possible. if the pointy thing has a hole in the butt end, use that to also secure to shaft to avoid slippage.
now, i say point thing, because i'd rather make something REALLY sharp and pointy out of anything but my knife. one could make several 1-2 foot long mini spikes (think vampire killing buffy style) out of the hardest wood you can find, harden in fire if possible. that's tough stuff... have a have with that little arrangement of sticks as above on the end. but don't terribly secure the pointy bit to the shaft... it's a slip in, not unlike an atlatl. potentially, if you're going after game, you throw, you hit, the shaft fall off, prey is wounded and runs off, you grab shaft (of course you have two, right?) reload a point, keep going.
for fish or other game like frogs/etc, just make a trident with three little wood points.
don't throw your knives in the woods! (they have a bad habit of coming back).
bladite