using Sitecore.Data.Items;

using Sitecore.Layouts;

...

public static string GetRenderingParameters(string renderingid)
{
  // convert path to ID. May cause exceptions
  renderingid = Sitecore.Context.Database.Items[renderingid].ID.ToString();

  // get current item.
  Item item = Sitecore.Context.Item;
  // get current device.
  DeviceItem device = Sitecore.Context.Device;

  // get list of rederings for the item.
  RenderingReference[] renderings;   
  renderings = item.Visualization.GetRenderings(device, true);

  // find appropriate rendering reference.
  foreach (RenderingReference reference in renderings)
  {
    if (reference.RenderingItem != null)
    {
      if (reference.RenderingItem.ID.ToString() == renderingid)
      {
        return reference.Settings.Parameters;
      }
    }
  }
  // return empty string if nothing found.
  return string.Empty;
}