[Tex/LaTex] Left Justification of Table Caption in Adjustbox Package

Question

I want to change the position of table caption to left, i'd appreciate if someone could help,

\documentclass[12pt,a4paper]{article} 
\usepackage{caption} 
\captionsetup[table]{singlelinecheck=false}
\usepackage{adjustbox}
\captionsetup[table]{
    labelsep = newline,
    textfont = sc, 
    name = TABLE, 
    justification=justified,
    singlelinecheck=false,%%%%%%% a single line is centered by default
    labelsep=colon,%%%%%%
    skip = \medskipamount}
\begin{document}


\begin{table}
    \centering
    \caption{Variables and Definitions}\label{table:2}
    \begin{adjustbox}{center}
        \begin{tabular}{ l p{10.5cm} p{3cm}}
            \hline\hline   
            Variables &  Definition & Source \\  \hline\hline   
            POV    & Measured as Poverty Headcount ratio at \$ 2 a day           & WDI                    \\   
            PG     & Measured as Poverty gap at \$ 2 a day       & WDI                   \\  
            GINI   & Income Inequality, natural log of GINI coefficient  &  WDI     \\   \hline                              
            \hline\hline    
            \multicolumn{3}{l}{%
                \begin{minipage}{16cm}%
                    \tiny Note: $+$The World Bank, World Development Indicators (WDI). %
                \end{minipage}%
            }\\
        \end{tabular}
    \end{adjustbox}
\end{table}

\end{document}

Answer 1

You don't need adjustboxfor this table, if you simply use the l specifier for the last column. It all can be done with the threeparttable and tablenotes environments. I also took the liberty to replace your \hlines with rules from the booktabs package, and add some vertical padding to the rows with \addlinespace from the same package:

\documentclass[12pt,a4paper]{article}
\usepackage[showframe]{geometry}
\usepackage{caption}
\captionsetup[table]{singlelinecheck=false}
\usepackage{adjustbox}
\captionsetup[table]{
labelsep = newline,
textfont = sc,
name = TABLE,
justification=justified,
singlelinecheck=false,%%%%%%% a single line is centered by default
labelsep=colon,%%%%%%
skip = \medskipamount}
\usepackage{booktabs, threeparttable}

\begin{document}

\begin{table}
  \centering
  \begin{threeparttable}[online]
    \caption{Variables and Definitions}\label{table:2}
    \begin{tabular}{lp{10.5cm}l}
      \toprule\midrule
      Variables & Definition & Source \\
      \midrule\midrule
      POV & Measured as Poverty Headcount ratio at \$ 2 a day & WDI \\
      \addlinespace
      PG & Measured as Poverty gap at \$ 2 a day & WDI \\
      \addlinespace
      GINI & Income Inequality, natural log of GINI coefficient & WDI \\
      \midrule \bottomrule
    \end{tabular}
    \begin{tablenotes}[online]\medskip
      \tiny \item[Note:] $+$The World Bank, World Development Indicators (WDI). %
    \end{tablenotes}
  \end{threeparttable}
\end{table}

\end{document}