Attempted Knockmannon on Friday last and followed jackill's excellent instructions. However, when I followed the line of wooden poles leading upward from the third gate I could find no easy way into the forest. It's as if the forest is surrounded by a wall-like rampart of brambles and briars - fortress-like, almost.
Went along the forestry edge away to my right, but was gradually going downhill with no obvious entry to the trees. So off I went exploring the forestry edge to the left of the poles. This led to the highest open ground on Knockmannon, accessed by hopping two very adjacent fences.
Lo and behold, at the very high point of this open area there stands a mound of earth (detritus from nearby mast erection, probably) - this is right up against the forest edge. By balancing on one leg atop this mound I reckoned I was at least on a par with whatever high point lurks in the forest within.
I had a good gander all along the forest's edge for a few hundred metres in either direction and found it impenetrable so that good old mound became my high point for this trip. Incidentally, the field to the left of the poles (as you ascend) was home that day to a rather feisty herd of bullocks - avoid them if you can. I was lucky, they were way down at the far end of the field and by the time thay came prancing up to me I was at the fence within a quick leap to safety, phew. Linkback: https://mountainviews.ie/summit/1126/comment/24260/