\begin{tikzpicture}
\begin{axis}[
name=plot2,
%at=(plot1.below south east), anchor=above north east, xshift=1cm,
axis lines*=middle,
enlargelimits = true, clip=false,
scale only axis,
axis line style={->,>=stealth, shorten >= 0pt},
xlabel={$n$},
ylabel={$x[n]$},
every axis x label/.style={
	at={(ticklabel* cs:1)},
	xshift=-0.2cm,
	anchor=north,
},
every axis y label/.style={
	at={(ticklabel* cs:1)},
	xshift=0.4cm,
	anchor=south,
},
every outer x axis line/.append style={white!15!black},
every x tick label/.append style={font=\color{white!15!black}},
xmin=0, xmax=12,
ymin=-2, ymax=2,
xtick={0, ..., 11},
xticklabel style={xshift=-0.15cm},
every outer y axis line/.append style={white!15!black},
every y tick label/.append style={font=\color{white!15!black}},
legend style={draw=white!15!black,fill=white,legend cell align=left, at={(axis cs: 1.05, -5)}}]

\addplot [smooth, color=black!20, solid, line width=2pt, domain=0:10.2, samples=31] {pretty_func(x)}; 

\addplot[ycomb, mark=*, fill=white, mark options={scale=1.5, fill=white}, line width=1.5pt, domain=0:10, samples=11] {pretty_func(x)};

\node[above] at (axis cs: 11, 1) {\large ?};
\end{axis}
\end{tikzpicture}