The Barska 3-9x40mm Huntmaster Rifle Scope could be mounted to a Knight Muzzle Loader if you have a compatible base and rings. The ring mounts at the link below should work with your muzzle loader and this scope.
https://www.opticsplanet.com/talley-lightweight-alloy-scope-mounts-for-knight-thompson-center-tikka.html?_iv_gun-make=knight-rifles&_iv_gun-model=knight-mountaineer
The Barska 3-9x40mm Huntmaster Rifle Scope could be mounted to a Marlin 336. However, the correct scope would depend on personal preference. If you want to use the Barska 3-9x40mm Huntmaster Rifle Scope on a Marlin 336 the rings at the link below will work.
https://www.opticsplanet.com/talley-lightweight-alloy-scope-mounts-for-anschutz-legendary-marlin-montana-winc.html?_iv_parent-gun-make=marlin&_iv_gun-make=marlin&_iv_gun-model=marlin-model-336,marlin-model-1895&_iv_tube-diameter=1-in&_iv_code=9E-MT-SMALMW-940336&_iv_ring-height=medium
No, you will need to acquire either rings or a mount separately.