。
She knows a lot of English vocabulary.
Literal
She [topic-は] English [genitive-の] vocabulary [object-を] a lot is-knowing.
知っている (rather than plain 知る) is the standard way to say 'knows' — 知る is a change-of-state verb ('to come to know'), and ~ている here marks the resulting state of having learned. The negative is 知らない, not 知っていない: an exception to the usual ~ている negation pattern, since the negative carries a clear 'doesn't know' reading without the auxiliary. 語彙 ('vocabulary') is a kanji compound somewhat opaque on inspection — 語 is straightforward ('word'), but 彙 ('group, collection') is a rare character that almost only appears in this word.