You can do as follows :
TCollection_ExtendedString aTCoText("Text");
gp_Pnt aPnt OrigineDimZT(0,0,0);
aPresentation= new Prs3d_Presentation(aContext->CurrentViewer()->Viewer());
Handle(Prs3d_TextAspect) aTextAspect= new Prs3d_TextAspect();
aTextAspect->SetFont(Graphic3d_NOF_ASCII_COMPLEX);
aTextAspect->SetHeight(6);
aTextAspect->SetColor(Quantity_NOC_SNOW);
aTextAspect->SetSpace(20);
Prs3d_Text::Draw(aPresentation,aComeAspect,aText, OrigineCome);
Prs3d_Text::Draw(aPresentation,aTextAspect,aTCoText, OrigineDimZT);
aPresentation->Display();
Denis