Skirting board filler chipping off
Are you trying to achieve a perfect seam or just looking to hide the gap?
You can fill it with paintable caulk/silicone and proceed with painting.
Yes, gloss paint needs to be scuffed up so that new paint can adhere properly unless you are applying an oil-based paint.
If you want to turn this painting project into a painful multi-day renovation then remove the skirting, sand or scrape down the protruding paint from both the wall and skirting, patch the wall with mud, sand, prime, re-attach the skirting, apply paintable caulk or silicone, and finally paint the skirting and wall.