First, get the list of all existing assets using the following:
return getAssetRegistry('org.example.Vehicle')
  .then(function (vehicleAssetRegistry) {
    // Get all of the vehicles in the vehicle asset registry.
    return assetRegistry.getAll();
  })
This will display all the assets present along with their string ID
And then get the particular asset:
return getAssetRegistry('org.example.Vehicle')
  .then(function (vehicleAssetRegistry) {
    // Get the specific vehicle from the vehicle asset registry.
    return assetRegistry.get('<String ID>');
  })