O'h I'm sorry.
In API guide described API_WallRelation, that contains needed polygon.
For my aim this code works.
API_Polygon* poly;
API_WallRelation relData;
poly = &relData.connPoly;
for (j = 1; j <= poly->nSubPolys; j++) {
begInd = (*relData.pends)[j - 1] + 1;
endInd = (*relData.pends);
for (i = begInd; i < endInd; i++) {
begC = (*relData.coords);
endC = (*relData.coords)[i + 1];
}
}