Best first cut into 22CM-23CM length, first grind the two needles. Unless the wood happens to be only 10 or so CM long, then it can only be sharpened separately.
With a file or coarse sandpaper (preferably 80 grit) to grind out the two needles, grinding the hand holding the needles for rotary action.
The length of the needles can be seen below, where I sharpened the needles, and I feel that this shape is quite comfortable for knitting. The file to file the needles can be seen in the link above, I use 80 grit sandpaper to grind, with sandpaper it is easier to control the shape of the needles, more suitable for novice knitters.