Here are a couple of quick solutions that come to my mind, probably there are much better ones and probably there is some Chinese specific thing for this.

#let dotted1(c) = context {
  let (width: wd, height: hd) = measure(".")
  box(place(dx: .5 * wd, dy: -.7 * hd, "."))
  c
}

#let dotted2(c) = context {
  let (width: wd, height: hd) = measure(".")
  box(stack(c, v(-.7 * hd), h(.5 * wd)   ".", v(-.3 * hd)))
}

a#dotted1[b]c

a#dotted2[b]c

You can experiment with math.attach also, but I think it's problematic because of #366. For example:

#let dotted3(c) = $attach(limits(upright(#c)), b: inline(dot))$

a#dotted3[b]b

Look how it's not the same "b".

Then again, try to find out whether there is something more specific for Chinese instead of these hacks, if it is so common to stress symbols like that there should be some kind of accent.