。
I've finally got the hang of kendo.
Literal
Finally kendo [genitive-の] breath [object-を] grasped.
呼吸をつかむ (literally 'to grasp the breath,' idiomatically 'to catch the rhythm/essence') is a productive idiom for any skill with an underlying rhythm — writing, dance, music, martial arts. ついに ('at last, finally') signals the completion of long effort. 剣道 ('the way of the sword,' kendo) is the modern Japanese martial art using bamboo swords (shinai). The sentence captures the satisfaction of finally clicking with the art after extensive training.