[RWD version 1 ] Not a pleasant experience, this climb, and while relatively short, in retrospect I would have undertaken a much longer route to avoid one section in particular.
The first 800m was an easy walk up a good forest track (enlivened by some autumnal colours) to where it swings I recommend that you continue along the track NNW as it turns back eventually to the SE and should take you to within 50m of the high point, although this will add about 3km to your outward journey. Alternatively you could take my ‘shortcut’. Where the track turns NNW, as suggested by fergalh, I continued up a narrow, boggy trail for about 50m, turned left for about 30m, then clambered up a steep bank to a thinly forested area. Unfortunately the ground underfoot was very uneven, swampy in parts and covered in long grass, heather, rotting trees and a variety of other vegetation, which made the next 200m ascent horribly unpleasant – a total slog that took me about 25 minutes to traverse. Eventually I emerged onto open hillside, covered in long grass with more uneven ground, which made for another long slog uphill. Eventually I veered into the forest, which was mature and allowed for relatively easy passage the last 50m to the ‘summit’, a clearing of sorts, although it was difficult to determine the exact high point. I tried and failed to find an alternate route down, and did locate a narrow, swampy trail that I followed for about 1km, but eventually had to descend through the rough ground the way I’d come up. I arrived back at the car saturated and bid Knockfune good riddance!