what you can do is assign a tag to your axes when you create them, and point back to them in your callback functions.
here's an example:
a = axes;
a.Tag = 'ax1';
b=axes;
b.Tag = 'ax2'
Now, within your callback:
a= findobj(gcf,'Tag','ax1');
b = findobj(gcf,'Tag','ax2');
plot(a,x,y)
plot(b,x2,y2)
if your axes are in the same function as your callback function, you dont need to assign any tags or look for them, just pass the handle as the first argument
plot(a,x,y)
plot(b,x2,y2)
