Silent Gear: 4.0.4
Silent's Gems: N/A
Silent Lib: 10.3.0
NeoForge: 21.1.66
Optifine Installed: No

Just change the c:tools/knives to c:tools/knife. This also apply to all other tools that use plural instead of singular tags

If you look at the Tool subgroup, Neoforge uses singular naming for the tools, not plural.
https://github.com/neoforged/NeoForge/blob/1.21.x/src/generated/resources/data/c/tags/item/tools.json

It also follow the Tag Conventions set by Neoforge and be compatible with other knife recipes.: neoforged/NeoForge#1498 (comment)