How to make column bold in array?

collcell seems to help here, passing the cell contents to a \user macro (with one argument) via the array-like column specification

. . . >{\collectcell\usermacro}c<{\endcollectcell} . . .

\documentclass{article}

\usepackage{amsmath,collcell}

\begin{document}

\[
  \begin{array}{ c c | >{\collectcell\boldsymbol}c<{\endcollectcell} c l c c l }
    X & Y & \neg & X & \rightarrow( & Y & \rightarrow & X)) \\
    \hline
    0 & 0 & 0 & 0 & 1 & 0 & 1 & 0 \\
    0 & 1 & 0 & 0 & 1 & 1 & 0 & 0 \\
    1 & 0 & 0 & 1 & 1 & 0 & 1 & 1 \\
    1 & 1 & 0 & 1 & 1 & 1 & 1 & 1
  \end{array}
\]

\end{document}

Another possibility, without collcell, is to use a short definition like this:

\def\bstart#1\bstop{\boldsymbol{#1}}

This way, you will be able to bypass the & character at the end of each cell of the array and get the required bold math symbols.

\documentclass{article}
\usepackage{amsmath,array}

\def\bstart#1\bstop{\boldsymbol{#1}}

\begin{document}

\[
  \begin{array}{ c c | >{\bstart} c <{\bstop} c l c c l }
    X & Y & \neg & X & \rightarrow( & Y & \rightarrow & X)) \\
    \hline
    0 & 0 & 0 & 0 & 1 & 0 & 1 & 0 \\
    0 & 1 & 0 & 0 & 1 & 1 & 0 & 0 \\
    1 & 0 & 0 & 1 & 1 & 0 & 1 & 1 \\
    1 & 1 & 0 & 1 & 1 & 1 & 1 & 1
  \end{array}
\]

\end{document}

Enable \boldmath, but for this we need to exit from math mode, issuing \boldmath and reentering math mode. This is more conveniently done with a new column type.

\documentclass{article}

\usepackage{amsmath,array}

\newcolumntype{C}{>{$\boldmath$}c}

\begin{document}

\[
  \begin{array}{ c c | C c l c c l }
    X & Y & \neg & X & \rightarrow( & Y & \rightarrow & X)) \\
    \hline
    0 & 0 & 0 & 0 & 1 & 0 & 1 & 0 \\
    0 & 1 & 0 & 0 & 1 & 1 & 0 & 0 \\
    1 & 0 & 0 & 1 & 1 & 0 & 1 & 1 \\
    1 & 1 & 0 & 1 & 1 & 1 & 1 & 1
  \end{array}
\]

\end{document}