The order you slot it is totally personal preference, just make sure you aim to get all of these skills.
Puncture morph. Weapons section, One Hand and Shield tree. Your melee taunt, every tank must use it.
Silver Bolts morph. Guild section, Fighters Guild tree. This will pull the enemies close to you, a great skill to group enemies.
Spirit Mender morph. Class section, Living Death tree. It will heal you, create a corpse and also take some of your damage, very useful.
Bone Totem Morph. Class section, Bone Tyrant tree. This is a great buff for your team, debuff for the enemies and also a stun.
Inner Fire morph. Guild section, Undaunted tree. Your ranged taunt, that will also activate a synergy for your group.
Pummeling Goliath (Ultimate):
Bone Goliath Transformation morph. Class section, Bone Tyrant tree. Awesome ultimate that increases your health by 30k and your attacks will give you resources.
Wall of Elements morph. Weapons section, Destruction Staff tree. Awesome AOE, with the frost staff it will chill enemies and do a nice damage. Keep this up all the time.
Grave Grasp morph. Class section, Bone Tyrant tree. This skill will snare, immobilize and stun enemies, depending on the area the enemies are on, and also debuff enemies, plus buff the healing your Spirit Guardian does.
Bitter Harvest morph. Class section, Bone Tyrant tree. This simply will give you a TON of ultimate, and also reduce your damage taken just by having it slotted.
Bone Armor morph. Class section, Bone Tyrant tree. A must have for every necromancer tank. This will give you Major Resolve and also pull enemies to you.
Boneyard morph. Class section, Gravelord tree. This is an AOE skill that does frost damage and also gives Major Breach to enemies, great for mob packs.
Aggressive Horn (Ultimate):
War Horn morph. Alliance War section, Assault tree. Standard tanking ultimate, it will increase your team damage and resources, it’s always useful.
Class: All Grave Lord passives. All Bone Tyrant passives. All Living Death passives.
Weapon: All Destruction and One Hand and Shield Passives.
Armor: All Heavy Armor passives.
Racial: All Racial passives.
Guild: All Undaunted Passives. Slayer and Banish the Wicked from Fighters Guild.
Craft: Medicinal Use from the Alchemy tree.