skim over emulsion

I need to skim this wall after replacing the corner bead. Its already skimmed and painted with matt emulsion which seems sound. I’ve sugar soaped and rinsed the wall. What else should I do before skimming with multifinish? Do I need to key it and PVA or something like that

I had some building work done and they put their foot through the ceiling near the pendant, so they cut that bit out and put a new square of board up , taped and skimmed it, feathering out to the painted ceiling, and painted. After a day or so the paint was bubbling off at the edges, and after...

I've been tucked up by a plasterer, scrim showing through the skim etc, on a sloping area of ceiling. I dug out a few spots, very thin. I remember the guy standing back from the job whilst he was doing the wall and saying that it didn't look too bad, and I had to agree that it didn't but I think...