。
She has a knack for sniffing out tax evasion.
Literal
She [topic-は] tax-evasion [object-を] sniff-out [nominalizer-の] [subject-が] is-skilled.
嗅ぎ出す is a compound verb 嗅ぐ ('smell, sniff') + 出す ('put out / bring out'); the productive ~出す pattern means 'do X out / start doing X' depending on context — here it's 'sniff out, detect by smelling.' Used metaphorically (as it is here for uncovering tax evasion), the smell metaphor maps neatly onto the English 'sniff out.' ~のが得意 is a parallel to ~のがうまい — both mean 'good at,' with 得意 sometimes carrying a sense of 'one's specialty.'