。
She'll probably get his sarcasm.
Literal
She [topic-は] his [genitive-の] sarcasm [subject-が] will-understand [probably-だろう].
わかる ('to understand, get') famously takes its 'understood thing' with が — 日本語がわかる ('understand Japanese'), 意味がわかる ('understand the meaning'). This が-marking is a hallmark of stative or potential-like predicates in Japanese. ~だろう adds conjecture: 'probably (will) understand.' 皮肉 ('sarcasm, irony') is built from 皮 ('skin') + 肉 ('flesh') — the etymology suggests 'cutting to the bone, biting words.'