WhoAmIRequest Class

Console.WriteLine("Enabling auditing on the organization and account entites.");

// Enable auditing on the organization.
// First, get the organization's ID from the system user record.
Guid orgId = ((WhoAmIResponse)_service.Execute(new WhoAmIRequest())).OrganizationId;

// Next, retrieve the organization's record.
Organization org = _service.Retrieve( Organization.EntityLogicalName, orgId, 
    new ColumnSet( new string[] {"organizationid", "isauditenabled"} )) as Organization;

// Finally, enable auditing on the organization.
bool organizationAuditingFlag = org.IsAuditEnabled.Value;
org.IsAuditEnabled = true;
_service.Update(org);

// Enable auditing on account entities.
bool accountAuditingFlag = EnableEntityAuditing(Account.EntityLogicalName, true);