。
She knows how to play the guitar.
Literal
She [topic-は] guitar [of-の] way-of-playing [object-を] knows.
The ~方 ('way of doing') template at work — the masu-stem of 弾く ('play') becomes ひき, then suffixes ~方 to form 弾き方 ('way of playing,' here written ひき方 with mixed kana/kanji). The whole noun phrase ギターのひき方 ('the way of playing guitar') functions as the object of 知っている ('know'). Subtly different from ギターを弾ける ('can play the guitar') — knowing the technique versus actually being able to perform.