manual-exercise-question-numbering.tex

\documentclass{article}
\usepackage{exercise}
\renewcommand{\QuestionNB}{(\alph{Question})\ }
\renewcommand{\theQuestion}{(\alph{Question})}
\begin{document}
\begin{ExerciseList}
  \Exercise{Exercise title}

  \ExeText
  Some exercise introduction
  \Question{First question}
  \Question{Second question}\label{q2}
  \Question{Third question (\textit{Hint}: use your answer to question~\ref{q2})}
\end{ExerciseList}
\end{document}