//Given a brep and a face index
const ON_Brep* brep;
const int face_index = 0;
ON_SimpleArray<int> face_ti_list; //trims indeces list
ON_SimpleArray<int> face_ei_list; //edges indeces list

//Get the BrepFace of the given index
const ON_BrepFace* face = brep->Face(face_index);
if( 0 == face )
  return false;

//Get the loop of the face
for( int fli = 0; fli < face->LoopCount(); fli++ )
{
  const ON_BrepLoop* loop = face->Loop( fli );
  if( 0 == loop )
    continue;

  for( int lti = 0; lti < loop->TrimCount(); lti++ )
  {
    //Find the trim
    const ON_BrepTrim* trim = loop->Trim( lti );
    if( 0 == trim )
      continue;
    face_ti_list.Append( trim->m_trim_index );

    //Find the edge of that trim
    //Each trim has exactly one edge attached to it
    const ON_BrepEdge* edge = trim->Edge();
    if( 0 == edge )
      continue;
    face_ei_list.Append( edge->m_edge_index );
  }
}