PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX : <http://purl.org/net/schemarama#>
CONSTRUCT
{
  [] a :Warning;
    :message 'Concept [1] has no broader in scheme [2], and is not declared as top concept for this scheme.';
    :implicated ( ?x ?s );
  .
}
WHERE
{
  ?x skos:inScheme ?s.
  OPTIONAL 
  { 
    ?x skos:broader ?y.
    ?y skos:inScheme ?s.
  }.
  OPTIONAL
  {
    ?s skos:hasTopConcept ?z.
    FILTER ( ?z = ?x )
  }.
  FILTER ( !bound(?y) && !bound(?z) )
}