$re = '/(?:.|\s)*?(\\\\begin{.*?})(?:\s\\\\end{enumerate}\s*?)(\\\\questao.*)/';
$str = '\\begin{enumerate}
\\end{enumerate}
\\begin{enumerate}
\\end{enumerate}
\\begin{esse que eu quero 1}
\\end{enumerate}
\\questao{1}
\\begin{enumerate}
\\end{enumerate}
\\begin{enumerate}
\\end{enumerate}
\\begin{esse que eu quero 2}
\\end{enumerate}
\\questao{2}
\\begin{enumerate}
\\end{enumerate}
\\begin{enumerate}
\\end{enumerate}
\\begin{esse que eu quero 3}
\\end{enumerate}
\\questao{2}';
$subst = "$1\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php