zydis | lightweight x86/x86-64 disassembler

You already answered your own question with that Intel Knight's Corner link. KNC had its own version of what later became AVX-512, with incompatible machine-code encodings.

As documented in that Intel manual, KNC had instructions like jrcxz but for mask registers (which KNC and AVX-512 call k0..k7) to let you compare-and-branch in one instruction on a vector compare-into-mask result. JKZD - Jump near if mask is zero. It has 2 forms, jkzd k1, rel32 and jkzd k1, rel8

These are not standard instructions and don't appear in Intel's mainstream manuals (which include AVX-512). In AVX-512, you branch on a mask register value with ktest k1,k1 or kortest k1,k1 to set regular FLAGS, then use a regular branch condition. (With unrolling to get 2 vector compare results, you can branch on either of them being non-zero with kortest k1,k2 with 2 separate registers.)