Impossible, unless you limit your design choices:
there’s no way of knowing what pixel-position the cursor would be at, unless you’re using a fixed-width, fixed height 1 font-size text.
Using 60px Andale Mono in a square pixels comp, gave me characters that were always 36 px apart.
So this worked for me:
l=thisComp.layer("fixed width text");
i=thisComp.layer("fixed width text").text.animator("Animator 1").selector("Range Selector 1").end-1;
c=i;
l.position + [i*36,0]
But then it’s very tricky to know on what line of a multi-line text the current character is on.
Do you need a special shape for the cursor ? Why can’t it be done with a variant of the word-processor effect ?