When working with metadata through the API, the recommendation is to use the API rather than working with the item directly.
The API returns a well-defined data model of type AssetMetadata which contains the following properties and methods:

Property name	Type	Stampvalue	Description
Name	String	{stampvalue-asset:name}	The title of the asset.
Description	String	{stampvalue-asset:description}	The description of the asset.
AssetId	Int	{stampvalue-asset:assetid}	This is a unique id descending from the DAM Center.
AssetTypeId	Int	{stampvalue-asset:assettypeid}	This is a unique id, representing what type the asset is. E.g. The assettype for images is 4 and the assettype for videos is 1. This id can be mapped to an item using this location:system/modules/Digizuite/[silo id]/AssetTypeRoot
AssetTypeName	String	{stampvalue-asset:assettypename}	The name of the asset type.
AssetSiloId	String	{stampvalue-asset:assetsiloid}	The Sitecore itemId of the silo in which the asset is located.
AssetSiloName	String	{stampvalue-asset:assetsiloname}	The Sitecore item name of the silo in which the asset is located.
ImportedBy	String	{stampvalue-asset:importedby}	The name of the user who uploaded the asset.
CreatedDateTime	DateTime	{stampvalue-asset:createddatetime}	The upload date.
ChangedDateTime	DateTime	{stampvalue-asset:changeddatetime}	The change date.
Filesize	Long	{stampvalue-asset:filesize}	The file size of the original file in bytes.
FilesizeAbbreviated	String	{stampvalue-asset:filesizeabbreviated}	A more readable version of the file size ex. 606.34 KB
Extension	String	{stampvalue-asset:extension}	The extension of the original file.
VideoLength	String	{stampvalue-asset:videolength}	If the asset is of type video, then this is the length of the video.
VideoWidth	Int	{stampvalue-asset:videowidth}	The width of the original file.
VideoHeight	Int	{stampvalue-asset:videoheight}	The height of the original file.
VideoFps	Float	{stampvalue-asset:videofps}	The frames per seconds of the original file.
ImageWidth	Int	{stampvalue-asset:imagewidth}	The width of the original file.
ImageHeight	Int	{stampvalue-asset:imageheight}	The height of the original file.
ImageDpi	Int	{stampvalue-asset:imagedpi}	The dpi of the original file.
ThumbSmall	String	{stampvalue-asset:thumbsmall}	Url to DFS' System small thumbnail. The definition of this format (such as increasing resolution, for example) cannot be changed as it is used by the module.
Thumb	String	{stampvalue-asset:thumb}	Url to DFS' System thumbnail. The definition of this format (such as increasing resolution, for example) cannot be changed as it is used by the module.
Preview	String	{stampvalue-asset:preview}	Url to a specific image quality.
WebPreview	String	{stampvalue-asset:webpreview}	Url to a specific image quality.
RawUrl	String	{stampvalue-asset:rawurl}	Url to the source file. This will download the source file.
DynamicMetadata	IDictionary<string, string>	{stampvalue-asset:[enter metafieldId]}	This dictionary contains all the dynamic metafields from the DAM Center. The key is the MetafieldId of the metafield. All metafields can be found either in DAM Center or in this location: Sitecore:system/modules/Digizuite/[silo id]/MetaGroupRoot. If you use the stampvalue, it would look like this: {stampvalue-asset:54322}

Method name	Description	Example of return value
GetMediaUrl()	Returns the media URL for the source file.	/media/512ffeba519249ff866095d7a25846ec/1-source
GetMediaUrl(string mediaFormatId, int resizeWidth = 0, int resizeHeight = 0, bool keepAspectRatio = true, bool allowUpScale = false))	Returns a media URL for the specified quality (mediaFormatId). This gives the opportunity resize the image. By default the keepAspectRatio is true and allowUpScale is false.	/media/512ffeba519249ff866095d7a25846ec/1-50044/resize/100x0/options/keepaspectratio
GetDownloadUrl()	Returns the download URL for the source file.	/media/512ffeba519249ff866095d7a25846ec/1-source/options/download
GetDownloadUrl(string mediaFormatId)	Returns the download URL for the specified quality (mediaFormatId).	/media/512ffeba519249ff866095d7a25846ec/1-50044/options/download
GetDigizuiteStreamingUrl(string mediaFormatId)	Returns the direct streaming URL to Digizuite. Use this for streams, for instance video or images. Please note that using this bypasses the Sitecore cache. Furthermore, the link contains an access token, which expires after some period of time, where the default is 24 hours. Therefore do NOT make the URL static on your pages, since the access token will expire.	https://[DIGIZUITE URL]/Dmm3BWSV3/assetstream.aspx?assetid=23&mediaformatid=50052&destinationid=10010&accesskey=f0b020bc-81e3-4824-82e3-2e6c1d8f714c

Note about mediaFormatId. The valid ids are located at the following path: Sitecore → System → Modules → Digizuite → MetadaraRoot_0 → FormatRoot. It is the complete list of formats available in the Sitecore solution. A format contains different fields for instance MediaFormatId which is the id used in the methods described above.

To see an example of how metadata looks for a specific asset use the DAM for Sitecore Administration dashboard - DFS 10.0.0 - Asset metadata viewer.

4.1 How to retrieve metadata from an item placed in the silo bucket

In order to retrieve the metadata for the silo item, call the following pipeline: DFS.GetAssetMetadata
The GetAssetMetadataArgs takes AssetItemId which is of type Sitecore.Data.ID and ContextLanguage which is of type Sitecore.Globalization.Language.

See example below

var renderArgs = new GetAssetMetadataArgs { AssetItemId = item.ID, ContextLanguage = Sitecore.Context.Language };
CorePipeline.Run(PipelineNames.GetAssetMetadata, renderArgs);
if (renderArgs.AssetMetadata == null)
{
	return;
}
var name = renderArgs.AssetMetadata.Name;

4.2 How to retrieve metadata for the field type Asset

AssetField assetField = Sitecore.Context.Item.Fields["Asset"]; 
var name = assetField.AssetMetadata.Name;

4.3 How to retrieve metadata for the field type AssetLink

AssetlinkField assetLinkField = Sitecore.Context.Item.Fields["AssetLink"]; 
var name = assetLinkField.AssetMetadata.Name;

4.4 How to retrieve metadata for the field type AssetList

AssetlistField assetList = Sitecore.Context.Item.Fields["AssetList"];
if (assetList != null)
{
	foreach (var asset in assetList.Assets)
		{
		// To request the rendering html for the asset you call the
		// RenderAsset method. It returns an RenderFieldResult object
		var renderResultItem = asset.RenderAsset(); 
		var title = asset.AssetMetadata.Name;
		var id = asset.AssetMetadata.AssetId;
		var assetTypeId = asset.AssetMetadata.AssetTypeId;
		var assetTypeName = asset.AssetMetadata.AssetTypeName; 


		// Get dynamic metadata
		var someDynamicMetadata = asset.AssetMetadata["50343"];
	}
}

4.5 Update asset metadata not supported from code

Updating an items metadata is not supported from code. Use the editor in the DAM Explorer or Asset browser.