\documentclass{article}
%%..
%%Usage: \gettikzxy{(P)}{\px}{\py}
\makeatletter
\newcommand{\gettikzxy}[3]{%
  \tikz@scan@one@point\pgfutil@firstofone#1\relax
  \edef#2{\the\pgf@x}%
  \edef#3{\the\pgf@y}%
  \pgfmathparse{#2/28.3465} \let#2\pgfmathresult;
  \pgfmathparse{#3/28.3465} \let#3\pgfmathresult;
}
\makeatother
%%..
\begin{document}
 
%%..

\begin{tikzpicture}
   \coordinate (A) at (1,1);
   \coordinate (B) at (3,4);
   \coordinate (M) at ($(A)!0.5!(B)$);
   
   \gettizxy{(A)}{\ax}{\ay};
   \gettizxy{(B)}{\bx}{\by};
   \gettizxy{(M)}{\mx}{\my};
   
   \node at (A) {$A=(\ax,\ay)$};
   \node at (B) {$B=(\bx,\by)$};
   \node at (M) {$M=(\mx,\my)$};
\end{tikzpicture}
 
%%..
\end{document}