\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}
\usepackage{hyperref}
\usepackage{tikz}
\usepackage{wheelchart}
\usetikzlibrary{decorations.markings}
\usepackage{siunitx}
\usepackage{adjustbox}
\definecolor{blu}{RGB}{102,140,217}
\definecolor{giallo}{RGB}{255,153,0}
\definecolor{rosso}{RGB}{220,57,18}
\definecolor{viola}{RGB}{153,0,153}

\setlength{\parindent}{0pt}

\hypersetup{
    colorlinks=true,
    linkcolor=blue,
    citecolor=blue,
    filecolor=magenta,
    urlcolor=blue,
}

\begin{document}


% Insert Image at specified Position
The following \autoref{image0} is inserted at the specified position.

\begin{figure}[h]
    \centering
    \begin{tikzpicture}
        \wheelchart[
          counterclockwise,
          data=\WCperc,
          data style={shift={(0,0.1)}},
          gap=0.03,
          legend columns=2,
          legend row={\tikz\fill[\WCvarB,draw=black] (0,0) rectangle (0.3,0.3); & \WCvarC},
          legend={
            \node[anchor=north] at (0,-2.5) {%
              \begin{tabular}{*{2}{l@{ }l}}%
              \WClegend%
              \end{tabular}%
            };
          },
          lines=0.5,
          lines angle shift{1}=20,
          lines angle shift{3}=-20,
          lines ext=2,
          lines ext left anchor=base west,
          lines ext right anchor=base east,
          lines sep=-1,
          lines style={
            postaction=decorate,
            decoration={
              markings,
              mark=at position 0 with {
                \fill (0,0) circle[radius=0.1];
              }
            }
          },
          radius={0}{2},
          title=Open Source,
          title style={font=\bfseries}
        ]{
          50/viola/Ja,
          50/giallo/Nein
        }
        \end{tikzpicture}
        \caption{image}
        \label{image0}
\end{figure}

This Reference to \autoref{image0} was inserted below the figure at the specified position. \\\\


It turns out that to use subfig with tikz, you need an adjustbox!

\begin{figure}[h]
    \centering
    \begin{subfigure}[b]{0.3\textwidth}
        \begin{adjustbox}{width=\linewidth}
        \begin{tikzpicture}
            \wheelchart[
              counterclockwise,
              data=\WCperc,
              data style={shift={(0,0.1)}},
              gap=0.03,
              legend columns=2,
              legend row={\tikz\fill[\WCvarB,draw=black] (0,0) rectangle (0.3,0.3); & \WCvarC},
              legend={
                \node[anchor=north] at (0,-2.5) {%
                  \begin{tabular}{*{2}{l@{ }l}}%
                  \WClegend%
                  \end{tabular}%
                };
              },
              lines=0.5,
              lines angle shift{1}=20,
              lines angle shift{3}=-20,
              lines ext=2,
              lines ext left anchor=base west,
              lines ext right anchor=base east,
              lines sep=-1,
              lines style={
                postaction=decorate,
                decoration={
                  markings,
                  mark=at position 0 with {
                    \fill (0,0) circle[radius=0.1];
                  }
                }
              },
              radius={0}{2},
              title=Open Source,
              title style={font=\bfseries}
            ]{
              50/viola/Ja,
              50/giallo/Nein
            }
            \end{tikzpicture}
        \end{adjustbox}
    \end{subfigure}
    \hfill
    \begin{subfigure}[b]{0.3\textwidth}
        \begin{adjustbox}{width=\linewidth}
        \begin{tikzpicture}
            \wheelchart[
              counterclockwise,
              data=\WCperc,
              data style={shift={(0,0.1)}},
              gap=0.03,
              legend columns=2,
              legend row={\tikz\fill[\WCvarB,draw=black] (0,0) rectangle (0.3,0.3); & \WCvarC},
              legend={
                \node[anchor=north] at (0,-2.5) {%
                  \begin{tabular}{*{2}{l@{ }l}}%
                  \WClegend%
                  \end{tabular}%
                };
              },
              lines=0.5,
              lines angle shift{1}=20,
              lines angle shift{3}=-20,
              lines ext=2,
              lines ext left anchor=base west,
              lines ext right anchor=base east,
              lines sep=-1,
              lines style={
                postaction=decorate,
                decoration={
                  markings,
                  mark=at position 0 with {
                    \fill (0,0) circle[radius=0.1];
                  }
                }
              },
              radius={0}{2},
              title=Open Source,
              title style={font=\bfseries}
            ]{
              50/viola/Ja,
              50/giallo/Nein
            }
            \end{tikzpicture}
        \end{adjustbox}
    \end{subfigure}
    \hfill
    \begin{subfigure}[b]{0.3\textwidth}
        \begin{adjustbox}{width=\linewidth}
        \begin{tikzpicture}
            \wheelchart[
              counterclockwise,
              data=\WCperc,
              data style={shift={(0,0.1)}},
              gap=0.03,
              legend columns=2,
              legend row={\tikz\fill[\WCvarB,draw=black] (0,0) rectangle (0.3,0.3); & \WCvarC},
              legend={
                \node[anchor=north] at (0,-2.5) {%
                  \begin{tabular}{*{2}{l@{ }l}}%
                  \WClegend%
                  \end{tabular}%
                };
              },
              lines=0.5,
              lines angle shift{1}=20,
              lines angle shift{3}=-20,
              lines ext=2,
              lines ext left anchor=base west,
              lines ext right anchor=base east,
              lines sep=-1,
              lines style={
                postaction=decorate,
                decoration={
                  markings,
                  mark=at position 0 with {
                    \fill (0,0) circle[radius=0.1];
                  }
                }
              },
              radius={0}{2},
              title=Open Source,
              title style={font=\bfseries}
            ]{
              50/viola/Ja,
              50/giallo/Nein
            }
            \end{tikzpicture}
        \end{adjustbox}
    \end{subfigure}
\end{figure}

\pagebreak
\listoffigures


\end{document}