答案1
尽管我坚决同意@egreg:下划线强调的文字信息太多,但你正在使用的类的MWE:
\documentclass[a4paper,12pt]{extbook}
\usepackage[normalem]{ulem}
\usepackage{titlesec,blindtext}
\titleformat*{\paragraph}{}
\newcommand{\tmp}[1]{}
\let\tmp\paragraph
\renewcommand{\paragraph}[1]{\tmp{\textbf{#1}}}
\newcommand{\ulemparagraph}[1]{\tmp{\uline{\emph{#1}}}}
\begin{document}
\section{Section}
Section text
\ulemparagraph{Some other text}
\paragraph{Even more text}
\end{document}