The List of Possibilities is huge and this will depend on the current weakness of the creatures to elemental damage from the weapon. So to name a few possibilities of use. Note that some creatures can be weak to two types of elements but generally one of them outweighs the other being something like 105% weakness versus 120% weakness. There are no Sanguine Set (Knight's) Weapons with an Ice element, so it won't have a Hunt list on it.
Clubs:
Sanguine Cudgel (One Hand) - 46 Death
Sanguine Bludgeon (Two Hands) - 50 Earth
Swords:
Sanguine Blade (One Handed) - 46 Fire
Sanguine Razor (Two Hands) - 50 Energy
Axes:
Sanguine Hatchet (One Handed) - 46 Fire
Sanguine Battleaxe (Two Handed) - 50 Death
Creatures weak to the Earth element (I will mention medium and high level respawns only):
* Otherworld (Gold Token): Breach Brood, Dread Intruder, Sparkion, Reality Reaver
* Dwelling of the Forgotten (Warzone 09): Cave Chimera, Tremendous Tyrant, Varnished Diremaw
* Secret Library (Energy Section): Energetic Book, Energuardian Of Tales
* Furious Crater (Soul War): Cloak Of Terror, Courage Leech
* Darklight Core (Rotten Blood): Darklight Matter, Darklight Source, Darklight Striker, Walking Pillar
Creatures weak to the Fire element (I'll mention medium and high level respawns only):
* Antrum of the Fallen (Warzone 07): Afflicted Strider, Blemished Spawn
* Secret Library (Ice Section): Animated Feather, Icecold Book, Squid Warden
* Ebb and Flow (Soul War): Bony Sea Devil, Turbulent Elemental
* Rotten Wasteland (Soul War): Branchy Crawler, Rotten Golem
* Darklight Core (Rotten Blood): Darklight Matter, Darklight Source, Darklight Striker
Creatures weak to the Energy element (I will mention medium and high level respawns only):
* Ancient Ancestorial Grounds (Gray Island): Deathling Scout, Deathling Spellsinger
* Secret Library (Earth Section): Cursed Book, Ink Blob
* Rotten Wasteland (Soul War): Branchy Crawler, Rotten Golem
* Gloom Pillars (Rotten Blood): Converter, Darklight Construct
* Jaded Roots (Rotten Blood): Bloated Man-Maggot, Mycobiontic Beetle, Sopping Corpus
Creatures weak to the Death element (I'll mention medium and high level respawns only):
* Kilmaresh (Various locations): Lamassu, Crypt Warden, Sphinx, Feral Sphinx
* Secret Library (Energy Section): Brain Squid, Knowledge Elemental
* Furious Crater (Soul War): Cloak Of Terror, Courage Leech
* Rotten Wasteland (Soul War): Branchy Crawler, Rotten Golem
* Gloom Pillars (Rotten Blood): Converter, Darklight Construct
Taking into account only high level hunts (currently Rotten Blood), the Energy element seems to be the best to cover the locations, being very effective on Gloom Pillars and Jaded Roots. It also has an effect on Rotten Wasteland (Soul War).
So with this information I come to the obvious result that the Item Sanguine Razor (Sword/Two Hands) is currently the Best Elemental Damage weapon for Knight's (Energy). Also if the item is a Grand Sanguine it will have even better abilities.
Information sources for this research are Tibia Wiki pages.