。
She knows that issue well.
Literal
She [topic-は] that issue [object-を] well knows.
知っている is the standard way to say 'know / be familiar with' — Japanese treats knowing as a resulting state from a moment of learning, which is why 知る ('come to know') in plain present is rare and 知っている is the everyday form. Watch the asymmetry on the negative side, though: it flips back to plain 知らない, not 知っていない. よく ('well, often, much') here functions as an intensifier on the verb of knowing.