tDBさん、わかりやすい回答ありがとうございます。
おかげで、\hakoも回答を表示することができました。

２つ、わからないことがあります。

tDBさんのサンプルソースは、最後の\closeHakoKaiFile
が、全体の\end{enumerate}の後でした。
途中は小問の後だと思いますが、最後はどちらがいいのでしょうか。
どちらでもいいのでしょうか。

２つめは、\hakoの解答に\yakubunや\Yakubunを
入れるとエラーになります。

　箱の中以外では、表示されるようです。

アドバイスをお願いします。

\documentclass{jarticle}
\usepackage{emath,emathP,hako}
\usepackage{emathAe,emathEy}
\renewcommand{\labelenumi}{\framebox[1.2em][c]{\arabic{enumi}}~}% 大問
\renewcommand{\labelenumii}{(\arabic{enumii})}%                 小問

\begin{document}
\openKaiFile
\begin{enumerate}
\item　大問1
\kaitou{\def\Kaienumerate{edaenumerate}\def\Kaienumopt{<retusuu=2>}}

\begin{edaenumerate}

\item 小問1\kaitou{解答1}

\item 小問2\kaitou{$\bunsuu46$}

\item 小問3\kaitou{$\yakubun{4}{6}{2}{3}$}

\item 小問4\kaitou{$\Yakubun{4}{6}$}

\end{edaenumerate}

\item 大問2(穴埋め)
\kaitou{\inputHakoKaiFile}%
\hakosyokika
\openHakoKaiFile% ハコの解答を外部ファイルに書き出す初期化処理
\begin{enumerate}
\item 穴埋め1\Hako'\bunsuu46'

\item 穴埋め2\Hako'\yakubun{4}{6}{2}{3}'

\item 穴埋め3\Hako'\Yakubun{4}{6}'

\end{enumerate}
\closeHakoKaiFile% ハコの解答を外部ファイルに書き出す終了処理


\end{enumerate}
\closeKaiFile
\hrule

【解答】
\inputKaiFile
\end{document}

〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜
以下は,logです。

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(./test2.k1
! Use of \yakubun@ doesn't match its definition.
\@ifnextchar ...eserved@d =#1\def \reserved@a {#2}
                                                  \def \reserved@b {#3}\futu...
l.42 \end
         \Kaienumerate\protect \def \Kaienumerate{enumerate}\def\Kaienumopt{}
? x

▼関連発言
│
└◆8616:kaitouの使い方について [SHIGE] 02/17 14:16
　└◆8617:Re:kaitouの使い方について [tDB] 02/17 16:53
　　└◆8618:Re[2]:kaitouの使い方について [SHIGE] 02/17 23:38
　　　└◆8619:Re[3]:kaitouの使い方について [tDB] 02/18 08:24
　　　　└◆8620:Re[4]:kaitouの使い方(\hako) [SHIGE] 02/18 16:07
　　　　　└◆8621:Re[5]:kaitouの使い方(\hako) [tDB] 02/18 16:28
　　　　　　└◆8622:Re[6]:kaitouの使い方(\hako) [SHIGE] 02/18 17:51<-last