Something like this should work:
using mojoPortal.Business;
using mojoPortal.Web;
PageSettings childPage;
PageSettings parentPage;
string childPageURL;
string parentPageURL;
childPage = CacheHelper.GetPage(pageId); // or CacheHelper.GetCurrentPage() if running in the context of the page you want to query
string childPageURL = SiteUtils.GetPageUrl(childPage);
if (childPage.ParentId != -1)
{
parentPage = CacheHelper.GetPage(childPage.ParentId);
parentPageURL = SiteUtils.GetPageUrl(parentPage);
}