。
She talks like she knows everything about the world.
Literal
[topic-は] just-as this world [genitive-の] thing [object-を] anything is-knowing-[such-as-ような] mouth-uses.
口をきく literally 'use one's mouth' is an idiomatic verb for 'speak, talk, address others' — often with a connotation of speech style or attitude. 偉そうな口をきく ('talk like a big shot'), 生意気な口をきく ('talk back saucily') — the verb pairs with adjectives or nouns describing how someone is talking. この世の中 ('this world, in this world') uses 世の中 (literally 'inside the world,' Japanese for 'the world, society') — distinct from 世界 (the world as the planet, broader). The simile frame implies pretentious omniscience: she speaks as if she has the entire world figured out, even though she patently does not.