Use hold on to place multiple plots on the same axes. Always pair it with hold off when you are complete.
If you want to add points, that sounds like a job for scatter, not boxplot.
You will need to tweak your solution to work with the specific approach you take. Here's some code to perhaps get you started.
b = bar(rand(2,4));
hold on
x = ones(10,2).*b(2).XEndPoints;
boxchart(x(:),rand(20,1),"BoxWidth",0.15)
hold off
