documentclass{standalone}
usepackage{tikz}
  usetikzlibrary{positioning}
begin{document}
  begin{tikzpicture}
    path node(n1){node 1};
    path node[below=0pt of n1](n2){node 2};
    % following doesn't work
    path node[below=10pt of (5pt,5pt)](n3){node 3};
  end{tikzpicture}
end{document}