The thin profile of Veritas’ Striking Knife makes it pretty versatile but at the same time hard to sharpen. It’s very small so there’s little bevel to “feel” for and the blade material is bendy so it’s hard to keep in the exact same orientation while sharpening.
Consequently over time mine will loose its nice pointed end and flat sides and it can’t reach into tight corners. To help me re-establish a nice flat bevel I use a really simple “jig”, just a scrap of wood with two 25° slots cut into it.
The jig then holds the marking knife up against the flat side of my CBN wheel. The 220-grit finish from the wheel isn’t great so I then finish up with my usual honing routine.
This slot-in-a-block-of-wood type jig could be used against a normal bench grinder (front of wheel of course), belt sander, or even to hold the knife for hand-sharpening on stones.