I ‘sight read’ two keys in scales/arpeggios/WTC every morning as my warmup (practically have them memorized now so it’s not really sight reading anymore). I use the Alfred Masterworks edition by Willard Palmer, which is the best I found at being a true Urtext and performance edition (it’s comb bind!)
It’s conventionally notated as a regular dotted eighth and sixteenth (dotted quaver and semiquaver). The notation PjotrB has above is in ancillary staves above the figures as an alternative, with this note
NB) The performance of this fugue with “overdotting” throughout, suggested by Arnold Dolmetsch, as indicated in the staffs in light print, is controversial.
Further there is a note in the second bar, bass second beat
"In the manuscript of Anna Magdalena Bach (P202), there are alignment lines here and in many subsequent measures … since it is not known when or by whoem these lines were added, they do not contribute important evidence that over-dotting should not be used
And later they note that doing the overdotting in one voice (bass, third beat of bar 9) against sixteenths (semiquavers) in the treble is extremely controversial, though some artists do it. Anyhow it appears these are problematic and best avoided unless you’re a top drawer performer preparing this for performance.