how to plot the graph of octagonal fuzzy number in latex?

Just use pgfplots (I added some parameters you can play around with):

documentclass{standalone}
usepackage{pgfplots}
usetikzlibrary{math}
begin{document}
    begin{tikzpicture}
        tikzmath{
            real k;
            real a0;
            real a1;
            real a2;
            real a3;
            real a4;
            real a5;
            real a6;
            real a7;
            real a8;
            k=3.0;
            a0=-5.0;
            a1= -3.0;
            a2= 2.0;
            a3= 4.0;
            a4= 5.0;
            a5= 9.0;
            a6= 10.0;
            a7= 11.0;
            a8= 12.0;
            a9=14.0;
        };
    begin{axis} [grid=major,legend style={overlay},every axis plot post/.append style={mark=none}]
        addplot [domain = a0:a1,color=blue]
        {0};
        addplot [domain = a1:a2,color=blue]
        {k*(x-a1)/(a2-a1)};
        addplot [domain = a2:a3,color=blue]
        {k};
        addplot [domain = a3:a4,color=blue]
        {k + (1-k)*(x-a3)/(a4-a3)};
        addplot [domain = a4:a5,color=blue]
        {1};
        addplot [domain = a5:a6,color=blue]
        {k + (1-k)*(a6-x)/(a6-a5)};
        addplot [domain = a6:a7,color=blue]
        {k};
        addplot [domain = a7:a8,color=blue]
        {k*(a8-x)/(a8-a7)};
        addplot [domain = a8:a9,color=blue]
        {0};
        
    end{axis}
end{tikzpicture}
end{document}

Adding the specific x-coordinates can be done by adapting the so-called ticks:

documentclass{standalone}
usepackage{pgfplots}
usetikzlibrary{math}
begin{document}
    begin{tikzpicture}
        tikzmath{
            real k;
            real a0;
            real a1;
            real a2;
            real a3;
            real a4;
            real a5;
            real a6;
            real a7;
            real a8;
            k=3.0;
            a0=-5.0;
            a1= -3.0;
            a2= 2.0;
            a3= 4.0;
            a4= 6.0;
            a5= 9.0;
            a6= 11.0;
            a7= 13.0;
            a8= 15.0;
            a9= 17.0;
        };
    begin{axis} [grid=major,legend style={overlay},every axis plot post/.append style={mark=None},xtick={a1,a2,a3,a4,a5,a6,a7,a8},
            xticklabels={$a_1$,$a_2$,$a_3$,$a_4$,$a_5$,$a_6$,$a_7$,$a_8$}]
        addplot [domain = a0:a1,samples=2,color=blue]
        {0};
        addplot [domain = a1:a2,samples=2,color=blue]
        {k*(x-a1)/(a2-a1)};
        addplot [domain = a2:a3,samples=2,color=blue]
        {k};
        addplot [domain = a3:a4,samples=2,color=blue]
        {k + (1-k)*(x-a3)/(a4-a3)};
        addplot [domain = a4:a5,samples=2,color=blue]
        {1};
        addplot [domain = a5:a6,samples=2,color=blue]
        {k + (1-k)*(a6-x)/(a6-a5)};
        addplot [domain = a6:a7,samples=2,color=blue]
        {k};
        addplot [domain = a7:a8,samples=2,color=blue]
        {k*(a8-x)/(a8-a7)};
        addplot [domain = a8:a9,samples=2,color=blue]
        {0};
        
        %legend{$B^3_0(t)$,$B^3_1(t)$,$B^3_2(t)$,$B^3_3(t)$}
    end{axis}
end{tikzpicture}
end{document}