I used the \MakeUppercase command to capitalize the subsection title, but there are some letters that are not capitalized synchronously.
\documentclass[10pt,a4paper]{extbook}\usepackage{extsizes}\usepackage[utf8]{vietnam}\usepackage{amsmath,amssymb,yhmath,mathrsfs,fontawesome}\let\widering\relax\usepackage{antpolt}\usepackage{fontawesome}\usepackage{amsmath,amssymb,mathrsfs,maybemath,xlop,polynom,slashbox}\usepackage[tikz]{bclogo}\usepackage{enumerate}\usepackage{tkz-euclide}\usepackage{tikz-3dplot}\usepackage{tkz-tab,tkz-linknodes}\usetikzlibrary{shapes.geometric,arrows,calc,intersections,angles,patterns,snakes,arrows,decorations.pathmorphing,backgrounds,positioning,fit,petri,shapes.symbols}\usepackage{pgfplots}\pgfplotsset{compat=1.9}\usepackage[hidelinks,unicode]{hyperref}\usepackage{currfile}\usepackage[top=2cm, bottom=2cm, left=2cm, right=2cm] {geometry}\usepackage[hidelinks,unicode]{hyperref}\usepackage{currfile}\setcounter{secnumdepth}{4}\setcounter{tocdepth}{2}\usepackage{titlesec}\usepackage{titletoc}\renewcommand\thesection{\@arabic\c@section}\renewcommand\thesubsection{\@Alph\c@subsection}\renewcommand\thesubsubsection{\@arabic\c@subsubsection}\makeatletter\def\thechapter{\Roman{chapter}}\titlespacing{\chapter}{0pt}{-10pt}{20pt}\titleformat{\chapter}[frame]{\color{violet!80}\fontfamily{pbk}\selectfont}{\filright\normalsize\enspace \faGraduationCap~CHƯƠNG \Huge\thechapter\enspace}{.5cm}{\Huge\bfseries\filcenter\MakeUppercase}\def\thesection{\arabic{section}}\titleformat{\section}{\fontfamily{put}\selectfont\color{magenta}\Large}{\tikz[baseline=(char.base)]\node[shape=circle,draw,line width = 1pt,inner sep=1pt,fill=violet!10] (char){\Huge\textcolor{red}{\S\thesection}};}{0em}{\Huge\bfseries\filcenter\MakeUppercase}\def\thesubsection{\Alph{subsection}}\titleformat{\subsection}{\fontfamily{pbk}\selectfont\large\bfseries\color{magenta}}{ \hspace*{-2.2ex}\tikz[baseline=(char.base)]\node[shape=circle,draw,inner sep=2pt,fill=violet!10] (char){\textcolor{red}{\thesubsection}};}{.1em}{\large\bfseries\MakeUppercase}\def\thesubsubsection{\arabic{subsubsection}}\titleformat{\subsubsection}{\fontfamily{pbk}\selectfont\small\bfseries\color{magenta}}{ \hspace*{-2ex}\tikz[baseline=(char.base)] \node[shape=diamond,draw,inner sep=2pt,fill=violet!10] (char) {\textcolor{red}{\thesubsubsection}};}{-0.3em}{\bfseries\MakeUppercase}\begin{document}\chapter{MỆNH ĐỀ - TẬP HỢP}\section{TẬP HỢP}\subsection{Tóm tắt lý thuyết}\subsection{Các dạng toán và ví dụ}\subsection{Bài tập tự luận}\subsection{Câu hỏi trắc nghiệm khách quan}\end{document}`