There is no field which explicitly documents if IPv6 is enabled, but network adapters will have an IP in IPv6 format if it is enabled. The following report lists network interfaces from Windows computers that have an IPv6 address:
Select Top 1000000 tblAssets.AssetID,
  tblAssets.AssetName,
  tblAssets.IPAddress,
  tblAssets.Lastseen,
  tsysOS.Image As icon,
  tsysOS.OSname,
  tblNetwork.Description As [Network interface],
  tblNetwork.IPAddress As IPAddresses
From tblAssets
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysOS On tblAssets.OScode = tsysOS.OScode
  Inner Join tblNetwork On tblAssets.AssetID = tblNetwork.AssetID
Where tblNetwork.IPAddress Like '%:%' And tblAssetCustom.State = 1 And
  tblNetwork.IPEnabled = 1
Order By tblAssets.AssetName,
  [Network interface]