L=1;NP=3;
epsilon0=1;e=1;k=1/(4Pi*epsilon0);
charge[1]=-1;charge[2]=2;charge[3]=-2;
xq[1]=(1-2Random[])L;yq[1]=(1-2Random[])L;
xq[2]=(1-2Random[])L;yq[2]=(1-2Random[])L;
xq[3]=(1-2Random[])L;yq[3]=(1-2Random[])L;
q[i_]:=charge[i]*e;
V[x_,y_]:=Sum[(1/k)*q[i]/Sqrt[((x-xq[i])^2+(y-yq[i])^2)],{i,1,NP}];
DensityPlot[V[x,y],{x,-1,1},{y,-1,1},Mesh->10,MeshStyle->{Black,Dashed}]
ContourPlot[V[x,y],{x,-1,1},{y,-1,1},Mesh->10,MeshStyle->{Black,Dashed}]
Plot3D[V[x,y],{x,-1,1},{y,-1,1},Mesh->10,MeshStyle->{Black,Dashed}]