If the item is on a character, this will return the ID of the character that is holding the item.
Basic instance data for the item.
COMPONENT TYPE: ItemInstances
Common data for the item relevant to its non-instanced properties.
COMPONENT TYPE: ItemCommonData
Information specifically about the item's objectives.
COMPONENT TYPE: ItemObjectives
Information specifically about the perks currently active on the item.
COMPONENT TYPE: ItemPerks
Information about how to render the item in 3D.
COMPONENT TYPE: ItemRenderData
Information about the sockets of the item: which are currently active, what potential sockets you could have and the stats/abilities/perks you can gain from them.
COMPONENT TYPE: ItemSockets
Information about the computed stats of the item: power, defense, etc...
COMPONENT TYPE: ItemStats
Information about the talent grid attached to the item. Talent nodes can provide a variety of benefits and abilities, and in Destiny 2 are used almost exclusively for the character's "Builds".
COMPONENT TYPE: ItemTalentGrids
The response object for retrieving an individual instanced item. None of these components are relevant for an item that doesn't have an "itemInstanceId": for those, get your information from the DestinyInventoryDefinition.