On the map Knocknagapple looks like a very quick and easy excursion from the Ballaghisheen Pass (671792 A) and so it (largely) proves, but there's a fair amount of outcropping rock to be tackled/outflanked, and a smidge of bog. A fence follows a line based upon (but not slavishly following) the ridge up to the top. If continuing to the NW Top it's worth bearing in mind that said fence pursues a rather 'athletic' line down to the connecting gap, and it's wise to descend a little way to the left or right. In the picture, taken from the facing slope of Knocknacusha across the pass, an Opel Corsa provides some scale (if you can see it). Linkback: https://mountainviews.ie/summit/562/comment/3772/