。
Whenever the chance arises, that guy acts like he knows everything.
Literal
That-guy [topic-は] something-[if-かと言うと] know-it-all-pretending [object-を] does.
何かと言うと is a fixed adverbial phrase meaning 'whenever the occasion arises', 'at every opportunity' — literally 'if you ask what (triggers him), it is...'. 知ったかぶり is a compound noun from 知った (past of 知る, 'knew') + ふり ('pretense') = 'pretending to have known', with the productive rendaku changing ふり → ぶり. As a behavior it's looked down on — the English 'know-it-all' has the same flavor.